cpython/Doc/reference/compound_stmts.rst

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.. _compound:
*******************
Compound statements
*******************
.. index:: pair: compound; statement
Compound statements contain (groups of) other statements; they affect or control
the execution of those other statements in some way. In general, compound
statements span multiple lines, although in simple incarnations a whole compound
statement may be contained in one line.
The :keyword:`if`, :keyword:`while` and :keyword:`for` statements implement
traditional control flow constructs. :keyword:`try` specifies exception
handlers and/or cleanup code for a group of statements, while the
:keyword:`with` statement allows the execution of initialization and
finalization code around a block of code. Function and class definitions are
also syntactically compound statements.
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.. index::
single: clause
single: suite
single: ; (semicolon)
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A compound statement consists of one or more 'clauses.' A clause consists of a
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header and a 'suite.' The clause headers of a particular compound statement are
all at the same indentation level. Each clause header begins with a uniquely
identifying keyword and ends with a colon. A suite is a group of statements
controlled by a clause. A suite can be one or more semicolon-separated simple
statements on the same line as the header, following the header's colon, or it
can be one or more indented statements on subsequent lines. Only the latter
form of a suite can contain nested compound statements; the following is illegal,
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mostly because it wouldn't be clear to which :keyword:`if` clause a following
:keyword:`else` clause would belong::
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if test1: if test2: print(x)
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Also note that the semicolon binds tighter than the colon in this context, so
that in the following example, either all or none of the :func:`print` calls are
executed::
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if x < y < z: print(x); print(y); print(z)
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Summarizing:
.. productionlist:: python-grammar
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compound_stmt: `if_stmt`
: | `while_stmt`
: | `for_stmt`
: | `try_stmt`
: | `with_stmt`
: | `match_stmt`
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: | `funcdef`
: | `classdef`
: | `async_with_stmt`
: | `async_for_stmt`
: | `async_funcdef`
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suite: `stmt_list` NEWLINE | NEWLINE INDENT `statement`+ DEDENT
statement: `stmt_list` NEWLINE | `compound_stmt`
stmt_list: `simple_stmt` (";" `simple_stmt`)* [";"]
.. index::
single: NEWLINE token
single: DEDENT token
pair: dangling; else
Note that statements always end in a ``NEWLINE`` possibly followed by a
``DEDENT``. Also note that optional continuation clauses always begin with a
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keyword that cannot start a statement, thus there are no ambiguities (the
'dangling :keyword:`else`' problem is solved in Python by requiring nested
:keyword:`if` statements to be indented).
The formatting of the grammar rules in the following sections places each clause
on a separate line for clarity.
.. _if:
.. _elif:
.. _else:
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The :keyword:`!if` statement
============================
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Merged revisions 59703-59773 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r59704 | christian.heimes | 2008-01-04 04:15:05 +0100 (Fri, 04 Jan 2008) | 1 line Moved include "Python.h" in front of other imports to silence a warning. ........ r59706 | raymond.hettinger | 2008-01-04 04:22:53 +0100 (Fri, 04 Jan 2008) | 10 lines Minor fix-ups to named tuples: * Make the _replace() method respect subclassing. * Using property() to make _fields read-only wasn't a good idea. It caused len(Point._fields) to fail. * Add note to _cast() about length checking and alternative with the star-operator. ........ r59707 | jeffrey.yasskin | 2008-01-04 09:01:23 +0100 (Fri, 04 Jan 2008) | 3 lines Make math.{floor,ceil}({int,long}) return float again for backwards compatibility after r59671 made them return integral types. ........ r59709 | christian.heimes | 2008-01-04 14:21:07 +0100 (Fri, 04 Jan 2008) | 1 line Bug #1713: posixpath.ismount() claims symlink to a mountpoint is a mountpoint. ........ r59712 | lars.gustaebel | 2008-01-04 15:00:33 +0100 (Fri, 04 Jan 2008) | 5 lines Issue #1735: TarFile.extractall() now correctly sets directory permissions and times. (will backport to 2.5) ........ r59714 | andrew.kuchling | 2008-01-04 15:47:17 +0100 (Fri, 04 Jan 2008) | 1 line Update links to bug/patch tracker ........ r59716 | christian.heimes | 2008-01-04 16:23:30 +0100 (Fri, 04 Jan 2008) | 1 line Added interface to Windows' WSAIoctl and a simple example for a network sniffer. ........ r59717 | christian.heimes | 2008-01-04 16:29:00 +0100 (Fri, 04 Jan 2008) | 1 line And here is the rest of Hirokazu Yamamoto's patch for VS6.0 support. Thanks Hiro! ........ r59719 | christian.heimes | 2008-01-04 16:34:06 +0100 (Fri, 04 Jan 2008) | 1 line Reverted last transaction. It's the wrong branch. ........ r59721 | christian.heimes | 2008-01-04 16:48:06 +0100 (Fri, 04 Jan 2008) | 1 line socket.ioctl is only available on Windows ........ r59722 | andrew.kuchling | 2008-01-04 19:24:41 +0100 (Fri, 04 Jan 2008) | 1 line Fix markup ........ r59723 | andrew.kuchling | 2008-01-04 19:25:05 +0100 (Fri, 04 Jan 2008) | 1 line Fix markup ........ r59725 | guido.van.rossum | 2008-01-05 01:59:59 +0100 (Sat, 05 Jan 2008) | 3 lines Patch #1725 by Mark Dickinson, fixes incorrect conversion of -1e1000 and adds errors for -0x. ........ r59726 | guido.van.rossum | 2008-01-05 02:21:57 +0100 (Sat, 05 Jan 2008) | 2 lines Patch #1698 by Senthil: allow '@' in username when parsed by urlparse.py. ........ r59727 | raymond.hettinger | 2008-01-05 02:35:43 +0100 (Sat, 05 Jan 2008) | 1 line Improve namedtuple's _cast() method with a docstring, new name, and error-checking. ........ r59728 | raymond.hettinger | 2008-01-05 03:17:24 +0100 (Sat, 05 Jan 2008) | 1 line Add error-checking to namedtuple's _replace() method. ........ r59730 | fred.drake | 2008-01-05 05:38:38 +0100 (Sat, 05 Jan 2008) | 2 lines clean up a comment ........ r59731 | jeffrey.yasskin | 2008-01-05 09:47:13 +0100 (Sat, 05 Jan 2008) | 11 lines Continue rolling back pep-3141 changes that changed behavior from 2.5. This round included: * Revert round to its 2.6 behavior (half away from 0). * Because round, floor, and ceil always return float again, it's no longer necessary to have them delegate to __xxx___, so I've ripped that out of their implementations and the Real ABC. This also helps in implementing types that work in both 2.6 and 3.0: you return int from the __xxx__ methods, and let it get enabled by the version upgrade. * Make pow(-1, .5) raise a ValueError again. ........ r59736 | andrew.kuchling | 2008-01-05 16:13:49 +0100 (Sat, 05 Jan 2008) | 1 line Fix comment typo ........ r59738 | thomas.heller | 2008-01-05 18:15:44 +0100 (Sat, 05 Jan 2008) | 1 line Add myself. ........ r59739 | georg.brandl | 2008-01-05 18:49:17 +0100 (Sat, 05 Jan 2008) | 2 lines Fix C++-style comment. ........ r59742 | georg.brandl | 2008-01-05 20:28:16 +0100 (Sat, 05 Jan 2008) | 2 lines Remove with_statement future imports from 2.6 docs. ........ r59743 | georg.brandl | 2008-01-05 20:29:45 +0100 (Sat, 05 Jan 2008) | 2 lines Simplify index entries; fix #1712. ........ r59744 | georg.brandl | 2008-01-05 20:44:22 +0100 (Sat, 05 Jan 2008) | 2 lines Doc patch #1730 from Robin Stocker; minor corrections mostly to os.rst. ........ r59749 | georg.brandl | 2008-01-05 21:29:13 +0100 (Sat, 05 Jan 2008) | 2 lines Revert socket.rst to unix-eol. ........ r59750 | georg.brandl | 2008-01-05 21:33:46 +0100 (Sat, 05 Jan 2008) | 2 lines Set native svn:eol-style property for text files. ........ r59752 | georg.brandl | 2008-01-05 21:46:29 +0100 (Sat, 05 Jan 2008) | 2 lines #1719: capitalization error in "UuidCreate". ........ r59753 | georg.brandl | 2008-01-05 22:02:25 +0100 (Sat, 05 Jan 2008) | 2 lines Repair markup. ........ r59754 | georg.brandl | 2008-01-05 22:10:50 +0100 (Sat, 05 Jan 2008) | 2 lines Use markup. ........ r59757 | christian.heimes | 2008-01-05 22:35:52 +0100 (Sat, 05 Jan 2008) | 1 line Final adjustments for #1601 ........ r59758 | guido.van.rossum | 2008-01-05 23:19:06 +0100 (Sat, 05 Jan 2008) | 3 lines Patch #1637: fix urlparse for URLs like 'http://x.com?arg=/foo'. Fix by John Nagle. ........ r59759 | guido.van.rossum | 2008-01-05 23:20:01 +0100 (Sat, 05 Jan 2008) | 2 lines Add John Nagle (of issue #1637). ........ r59765 | raymond.hettinger | 2008-01-06 10:02:24 +0100 (Sun, 06 Jan 2008) | 1 line Small code simplification. Forgot that classmethods can be called from intances. ........ r59766 | martin.v.loewis | 2008-01-06 11:09:48 +0100 (Sun, 06 Jan 2008) | 2 lines Use vcbuild for VS 2009. ........ r59767 | martin.v.loewis | 2008-01-06 12:03:43 +0100 (Sun, 06 Jan 2008) | 2 lines Package using VS 2008. ........ r59768 | martin.v.loewis | 2008-01-06 12:13:16 +0100 (Sun, 06 Jan 2008) | 2 lines Don't try to package msvcr90 for the moment. ........ r59769 | georg.brandl | 2008-01-06 15:17:36 +0100 (Sun, 06 Jan 2008) | 4 lines #1696393: don't check for '.' and '..' in ntpath.walk since they aren't returned from os.listdir anymore. Reported by Michael Haggerty. ........ r59770 | georg.brandl | 2008-01-06 15:27:15 +0100 (Sun, 06 Jan 2008) | 3 lines #1742: don't raise exception on os.path.relpath("a", "a"), but return os.curdir. Reported by Jesse Towner. ........ r59771 | georg.brandl | 2008-01-06 15:33:52 +0100 (Sun, 06 Jan 2008) | 2 lines #1591: Clarify docstring of Popen3. ........ r59772 | georg.brandl | 2008-01-06 16:30:34 +0100 (Sun, 06 Jan 2008) | 2 lines #1680: fix context manager example function name. ........ r59773 | georg.brandl | 2008-01-06 16:34:57 +0100 (Sun, 06 Jan 2008) | 2 lines #1755097: document default values for [].sort() and sorted(). ........
2008-01-06 12:59:19 -04:00
.. index::
! statement: if
Merged revisions 59703-59773 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r59704 | christian.heimes | 2008-01-04 04:15:05 +0100 (Fri, 04 Jan 2008) | 1 line Moved include "Python.h" in front of other imports to silence a warning. ........ r59706 | raymond.hettinger | 2008-01-04 04:22:53 +0100 (Fri, 04 Jan 2008) | 10 lines Minor fix-ups to named tuples: * Make the _replace() method respect subclassing. * Using property() to make _fields read-only wasn't a good idea. It caused len(Point._fields) to fail. * Add note to _cast() about length checking and alternative with the star-operator. ........ r59707 | jeffrey.yasskin | 2008-01-04 09:01:23 +0100 (Fri, 04 Jan 2008) | 3 lines Make math.{floor,ceil}({int,long}) return float again for backwards compatibility after r59671 made them return integral types. ........ r59709 | christian.heimes | 2008-01-04 14:21:07 +0100 (Fri, 04 Jan 2008) | 1 line Bug #1713: posixpath.ismount() claims symlink to a mountpoint is a mountpoint. ........ r59712 | lars.gustaebel | 2008-01-04 15:00:33 +0100 (Fri, 04 Jan 2008) | 5 lines Issue #1735: TarFile.extractall() now correctly sets directory permissions and times. (will backport to 2.5) ........ r59714 | andrew.kuchling | 2008-01-04 15:47:17 +0100 (Fri, 04 Jan 2008) | 1 line Update links to bug/patch tracker ........ r59716 | christian.heimes | 2008-01-04 16:23:30 +0100 (Fri, 04 Jan 2008) | 1 line Added interface to Windows' WSAIoctl and a simple example for a network sniffer. ........ r59717 | christian.heimes | 2008-01-04 16:29:00 +0100 (Fri, 04 Jan 2008) | 1 line And here is the rest of Hirokazu Yamamoto's patch for VS6.0 support. Thanks Hiro! ........ r59719 | christian.heimes | 2008-01-04 16:34:06 +0100 (Fri, 04 Jan 2008) | 1 line Reverted last transaction. It's the wrong branch. ........ r59721 | christian.heimes | 2008-01-04 16:48:06 +0100 (Fri, 04 Jan 2008) | 1 line socket.ioctl is only available on Windows ........ r59722 | andrew.kuchling | 2008-01-04 19:24:41 +0100 (Fri, 04 Jan 2008) | 1 line Fix markup ........ r59723 | andrew.kuchling | 2008-01-04 19:25:05 +0100 (Fri, 04 Jan 2008) | 1 line Fix markup ........ r59725 | guido.van.rossum | 2008-01-05 01:59:59 +0100 (Sat, 05 Jan 2008) | 3 lines Patch #1725 by Mark Dickinson, fixes incorrect conversion of -1e1000 and adds errors for -0x. ........ r59726 | guido.van.rossum | 2008-01-05 02:21:57 +0100 (Sat, 05 Jan 2008) | 2 lines Patch #1698 by Senthil: allow '@' in username when parsed by urlparse.py. ........ r59727 | raymond.hettinger | 2008-01-05 02:35:43 +0100 (Sat, 05 Jan 2008) | 1 line Improve namedtuple's _cast() method with a docstring, new name, and error-checking. ........ r59728 | raymond.hettinger | 2008-01-05 03:17:24 +0100 (Sat, 05 Jan 2008) | 1 line Add error-checking to namedtuple's _replace() method. ........ r59730 | fred.drake | 2008-01-05 05:38:38 +0100 (Sat, 05 Jan 2008) | 2 lines clean up a comment ........ r59731 | jeffrey.yasskin | 2008-01-05 09:47:13 +0100 (Sat, 05 Jan 2008) | 11 lines Continue rolling back pep-3141 changes that changed behavior from 2.5. This round included: * Revert round to its 2.6 behavior (half away from 0). * Because round, floor, and ceil always return float again, it's no longer necessary to have them delegate to __xxx___, so I've ripped that out of their implementations and the Real ABC. This also helps in implementing types that work in both 2.6 and 3.0: you return int from the __xxx__ methods, and let it get enabled by the version upgrade. * Make pow(-1, .5) raise a ValueError again. ........ r59736 | andrew.kuchling | 2008-01-05 16:13:49 +0100 (Sat, 05 Jan 2008) | 1 line Fix comment typo ........ r59738 | thomas.heller | 2008-01-05 18:15:44 +0100 (Sat, 05 Jan 2008) | 1 line Add myself. ........ r59739 | georg.brandl | 2008-01-05 18:49:17 +0100 (Sat, 05 Jan 2008) | 2 lines Fix C++-style comment. ........ r59742 | georg.brandl | 2008-01-05 20:28:16 +0100 (Sat, 05 Jan 2008) | 2 lines Remove with_statement future imports from 2.6 docs. ........ r59743 | georg.brandl | 2008-01-05 20:29:45 +0100 (Sat, 05 Jan 2008) | 2 lines Simplify index entries; fix #1712. ........ r59744 | georg.brandl | 2008-01-05 20:44:22 +0100 (Sat, 05 Jan 2008) | 2 lines Doc patch #1730 from Robin Stocker; minor corrections mostly to os.rst. ........ r59749 | georg.brandl | 2008-01-05 21:29:13 +0100 (Sat, 05 Jan 2008) | 2 lines Revert socket.rst to unix-eol. ........ r59750 | georg.brandl | 2008-01-05 21:33:46 +0100 (Sat, 05 Jan 2008) | 2 lines Set native svn:eol-style property for text files. ........ r59752 | georg.brandl | 2008-01-05 21:46:29 +0100 (Sat, 05 Jan 2008) | 2 lines #1719: capitalization error in "UuidCreate". ........ r59753 | georg.brandl | 2008-01-05 22:02:25 +0100 (Sat, 05 Jan 2008) | 2 lines Repair markup. ........ r59754 | georg.brandl | 2008-01-05 22:10:50 +0100 (Sat, 05 Jan 2008) | 2 lines Use markup. ........ r59757 | christian.heimes | 2008-01-05 22:35:52 +0100 (Sat, 05 Jan 2008) | 1 line Final adjustments for #1601 ........ r59758 | guido.van.rossum | 2008-01-05 23:19:06 +0100 (Sat, 05 Jan 2008) | 3 lines Patch #1637: fix urlparse for URLs like 'http://x.com?arg=/foo'. Fix by John Nagle. ........ r59759 | guido.van.rossum | 2008-01-05 23:20:01 +0100 (Sat, 05 Jan 2008) | 2 lines Add John Nagle (of issue #1637). ........ r59765 | raymond.hettinger | 2008-01-06 10:02:24 +0100 (Sun, 06 Jan 2008) | 1 line Small code simplification. Forgot that classmethods can be called from intances. ........ r59766 | martin.v.loewis | 2008-01-06 11:09:48 +0100 (Sun, 06 Jan 2008) | 2 lines Use vcbuild for VS 2009. ........ r59767 | martin.v.loewis | 2008-01-06 12:03:43 +0100 (Sun, 06 Jan 2008) | 2 lines Package using VS 2008. ........ r59768 | martin.v.loewis | 2008-01-06 12:13:16 +0100 (Sun, 06 Jan 2008) | 2 lines Don't try to package msvcr90 for the moment. ........ r59769 | georg.brandl | 2008-01-06 15:17:36 +0100 (Sun, 06 Jan 2008) | 4 lines #1696393: don't check for '.' and '..' in ntpath.walk since they aren't returned from os.listdir anymore. Reported by Michael Haggerty. ........ r59770 | georg.brandl | 2008-01-06 15:27:15 +0100 (Sun, 06 Jan 2008) | 3 lines #1742: don't raise exception on os.path.relpath("a", "a"), but return os.curdir. Reported by Jesse Towner. ........ r59771 | georg.brandl | 2008-01-06 15:33:52 +0100 (Sun, 06 Jan 2008) | 2 lines #1591: Clarify docstring of Popen3. ........ r59772 | georg.brandl | 2008-01-06 16:30:34 +0100 (Sun, 06 Jan 2008) | 2 lines #1680: fix context manager example function name. ........ r59773 | georg.brandl | 2008-01-06 16:34:57 +0100 (Sun, 06 Jan 2008) | 2 lines #1755097: document default values for [].sort() and sorted(). ........
2008-01-06 12:59:19 -04:00
keyword: elif
keyword: else
single: : (colon); compound statement
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The :keyword:`if` statement is used for conditional execution:
.. productionlist:: python-grammar
if_stmt: "if" `assignment_expression` ":" `suite`
: ("elif" `assignment_expression` ":" `suite`)*
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: ["else" ":" `suite`]
It selects exactly one of the suites by evaluating the expressions one by one
until one is found to be true (see section :ref:`booleans` for the definition of
true and false); then that suite is executed (and no other part of the
:keyword:`if` statement is executed or evaluated). If all expressions are
false, the suite of the :keyword:`else` clause, if present, is executed.
.. _while:
The :keyword:`!while` statement
===============================
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.. index::
! statement: while
keyword: else
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pair: loop; statement
single: : (colon); compound statement
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The :keyword:`while` statement is used for repeated execution as long as an
expression is true:
.. productionlist:: python-grammar
while_stmt: "while" `assignment_expression` ":" `suite`
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: ["else" ":" `suite`]
This repeatedly tests the expression and, if it is true, executes the first
suite; if the expression is false (which may be the first time it is tested) the
suite of the :keyword:`!else` clause, if present, is executed and the loop
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terminates.
.. index::
statement: break
statement: continue
A :keyword:`break` statement executed in the first suite terminates the loop
without executing the :keyword:`!else` clause's suite. A :keyword:`continue`
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statement executed in the first suite skips the rest of the suite and goes back
to testing the expression.
.. _for:
The :keyword:`!for` statement
=============================
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.. index::
! statement: for
keyword: in
keyword: else
pair: target; list
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pair: loop; statement
object: sequence
single: : (colon); compound statement
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The :keyword:`for` statement is used to iterate over the elements of a sequence
(such as a string, tuple or list) or other iterable object:
.. productionlist:: python-grammar
for_stmt: "for" `target_list` "in" `starred_list` ":" `suite`
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: ["else" ":" `suite`]
The ``starred_list`` expression is evaluated once; it should yield an
:term:`iterable` object. An :term:`iterator` is created for that iterable.
The first item provided
by the iterator is then assigned to the target list using the standard
rules for assignments (see :ref:`assignment`), and the suite is executed. This
repeats for each item provided by the iterator. When the iterator is exhausted,
the suite in the :keyword:`!else` clause,
if present, is executed, and the loop terminates.
2007-08-15 11:28:22 -03:00
.. index::
statement: break
statement: continue
A :keyword:`break` statement executed in the first suite terminates the loop
without executing the :keyword:`!else` clause's suite. A :keyword:`continue`
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statement executed in the first suite skips the rest of the suite and continues
with the next item, or with the :keyword:`!else` clause if there is no next
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item.
The for-loop makes assignments to the variables in the target list.
This overwrites all previous assignments to those variables including
those made in the suite of the for-loop::
for i in range(10):
print(i)
i = 5 # this will not affect the for-loop
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# because i will be overwritten with the next
# index in the range
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.. index::
builtin: range
Names in the target list are not deleted when the loop is finished, but if the
sequence is empty, they will not have been assigned to at all by the loop. Hint:
the built-in type :func:`range` represents immutable arithmetic sequences of integers.
For instance, iterating ``range(3)`` successively yields 0, 1, and then 2.
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.. versionchanged:: 3.11
Starred elements are now allowed in the expression list.
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2007-08-15 11:28:22 -03:00
.. _try:
The :keyword:`!try` statement
=============================
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Merged revisions 59703-59773 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r59704 | christian.heimes | 2008-01-04 04:15:05 +0100 (Fri, 04 Jan 2008) | 1 line Moved include "Python.h" in front of other imports to silence a warning. ........ r59706 | raymond.hettinger | 2008-01-04 04:22:53 +0100 (Fri, 04 Jan 2008) | 10 lines Minor fix-ups to named tuples: * Make the _replace() method respect subclassing. * Using property() to make _fields read-only wasn't a good idea. It caused len(Point._fields) to fail. * Add note to _cast() about length checking and alternative with the star-operator. ........ r59707 | jeffrey.yasskin | 2008-01-04 09:01:23 +0100 (Fri, 04 Jan 2008) | 3 lines Make math.{floor,ceil}({int,long}) return float again for backwards compatibility after r59671 made them return integral types. ........ r59709 | christian.heimes | 2008-01-04 14:21:07 +0100 (Fri, 04 Jan 2008) | 1 line Bug #1713: posixpath.ismount() claims symlink to a mountpoint is a mountpoint. ........ r59712 | lars.gustaebel | 2008-01-04 15:00:33 +0100 (Fri, 04 Jan 2008) | 5 lines Issue #1735: TarFile.extractall() now correctly sets directory permissions and times. (will backport to 2.5) ........ r59714 | andrew.kuchling | 2008-01-04 15:47:17 +0100 (Fri, 04 Jan 2008) | 1 line Update links to bug/patch tracker ........ r59716 | christian.heimes | 2008-01-04 16:23:30 +0100 (Fri, 04 Jan 2008) | 1 line Added interface to Windows' WSAIoctl and a simple example for a network sniffer. ........ r59717 | christian.heimes | 2008-01-04 16:29:00 +0100 (Fri, 04 Jan 2008) | 1 line And here is the rest of Hirokazu Yamamoto's patch for VS6.0 support. Thanks Hiro! ........ r59719 | christian.heimes | 2008-01-04 16:34:06 +0100 (Fri, 04 Jan 2008) | 1 line Reverted last transaction. It's the wrong branch. ........ r59721 | christian.heimes | 2008-01-04 16:48:06 +0100 (Fri, 04 Jan 2008) | 1 line socket.ioctl is only available on Windows ........ r59722 | andrew.kuchling | 2008-01-04 19:24:41 +0100 (Fri, 04 Jan 2008) | 1 line Fix markup ........ r59723 | andrew.kuchling | 2008-01-04 19:25:05 +0100 (Fri, 04 Jan 2008) | 1 line Fix markup ........ r59725 | guido.van.rossum | 2008-01-05 01:59:59 +0100 (Sat, 05 Jan 2008) | 3 lines Patch #1725 by Mark Dickinson, fixes incorrect conversion of -1e1000 and adds errors for -0x. ........ r59726 | guido.van.rossum | 2008-01-05 02:21:57 +0100 (Sat, 05 Jan 2008) | 2 lines Patch #1698 by Senthil: allow '@' in username when parsed by urlparse.py. ........ r59727 | raymond.hettinger | 2008-01-05 02:35:43 +0100 (Sat, 05 Jan 2008) | 1 line Improve namedtuple's _cast() method with a docstring, new name, and error-checking. ........ r59728 | raymond.hettinger | 2008-01-05 03:17:24 +0100 (Sat, 05 Jan 2008) | 1 line Add error-checking to namedtuple's _replace() method. ........ r59730 | fred.drake | 2008-01-05 05:38:38 +0100 (Sat, 05 Jan 2008) | 2 lines clean up a comment ........ r59731 | jeffrey.yasskin | 2008-01-05 09:47:13 +0100 (Sat, 05 Jan 2008) | 11 lines Continue rolling back pep-3141 changes that changed behavior from 2.5. This round included: * Revert round to its 2.6 behavior (half away from 0). * Because round, floor, and ceil always return float again, it's no longer necessary to have them delegate to __xxx___, so I've ripped that out of their implementations and the Real ABC. This also helps in implementing types that work in both 2.6 and 3.0: you return int from the __xxx__ methods, and let it get enabled by the version upgrade. * Make pow(-1, .5) raise a ValueError again. ........ r59736 | andrew.kuchling | 2008-01-05 16:13:49 +0100 (Sat, 05 Jan 2008) | 1 line Fix comment typo ........ r59738 | thomas.heller | 2008-01-05 18:15:44 +0100 (Sat, 05 Jan 2008) | 1 line Add myself. ........ r59739 | georg.brandl | 2008-01-05 18:49:17 +0100 (Sat, 05 Jan 2008) | 2 lines Fix C++-style comment. ........ r59742 | georg.brandl | 2008-01-05 20:28:16 +0100 (Sat, 05 Jan 2008) | 2 lines Remove with_statement future imports from 2.6 docs. ........ r59743 | georg.brandl | 2008-01-05 20:29:45 +0100 (Sat, 05 Jan 2008) | 2 lines Simplify index entries; fix #1712. ........ r59744 | georg.brandl | 2008-01-05 20:44:22 +0100 (Sat, 05 Jan 2008) | 2 lines Doc patch #1730 from Robin Stocker; minor corrections mostly to os.rst. ........ r59749 | georg.brandl | 2008-01-05 21:29:13 +0100 (Sat, 05 Jan 2008) | 2 lines Revert socket.rst to unix-eol. ........ r59750 | georg.brandl | 2008-01-05 21:33:46 +0100 (Sat, 05 Jan 2008) | 2 lines Set native svn:eol-style property for text files. ........ r59752 | georg.brandl | 2008-01-05 21:46:29 +0100 (Sat, 05 Jan 2008) | 2 lines #1719: capitalization error in "UuidCreate". ........ r59753 | georg.brandl | 2008-01-05 22:02:25 +0100 (Sat, 05 Jan 2008) | 2 lines Repair markup. ........ r59754 | georg.brandl | 2008-01-05 22:10:50 +0100 (Sat, 05 Jan 2008) | 2 lines Use markup. ........ r59757 | christian.heimes | 2008-01-05 22:35:52 +0100 (Sat, 05 Jan 2008) | 1 line Final adjustments for #1601 ........ r59758 | guido.van.rossum | 2008-01-05 23:19:06 +0100 (Sat, 05 Jan 2008) | 3 lines Patch #1637: fix urlparse for URLs like 'http://x.com?arg=/foo'. Fix by John Nagle. ........ r59759 | guido.van.rossum | 2008-01-05 23:20:01 +0100 (Sat, 05 Jan 2008) | 2 lines Add John Nagle (of issue #1637). ........ r59765 | raymond.hettinger | 2008-01-06 10:02:24 +0100 (Sun, 06 Jan 2008) | 1 line Small code simplification. Forgot that classmethods can be called from intances. ........ r59766 | martin.v.loewis | 2008-01-06 11:09:48 +0100 (Sun, 06 Jan 2008) | 2 lines Use vcbuild for VS 2009. ........ r59767 | martin.v.loewis | 2008-01-06 12:03:43 +0100 (Sun, 06 Jan 2008) | 2 lines Package using VS 2008. ........ r59768 | martin.v.loewis | 2008-01-06 12:13:16 +0100 (Sun, 06 Jan 2008) | 2 lines Don't try to package msvcr90 for the moment. ........ r59769 | georg.brandl | 2008-01-06 15:17:36 +0100 (Sun, 06 Jan 2008) | 4 lines #1696393: don't check for '.' and '..' in ntpath.walk since they aren't returned from os.listdir anymore. Reported by Michael Haggerty. ........ r59770 | georg.brandl | 2008-01-06 15:27:15 +0100 (Sun, 06 Jan 2008) | 3 lines #1742: don't raise exception on os.path.relpath("a", "a"), but return os.curdir. Reported by Jesse Towner. ........ r59771 | georg.brandl | 2008-01-06 15:33:52 +0100 (Sun, 06 Jan 2008) | 2 lines #1591: Clarify docstring of Popen3. ........ r59772 | georg.brandl | 2008-01-06 16:30:34 +0100 (Sun, 06 Jan 2008) | 2 lines #1680: fix context manager example function name. ........ r59773 | georg.brandl | 2008-01-06 16:34:57 +0100 (Sun, 06 Jan 2008) | 2 lines #1755097: document default values for [].sort() and sorted(). ........
2008-01-06 12:59:19 -04:00
.. index::
! statement: try
Merged revisions 59703-59773 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r59704 | christian.heimes | 2008-01-04 04:15:05 +0100 (Fri, 04 Jan 2008) | 1 line Moved include "Python.h" in front of other imports to silence a warning. ........ r59706 | raymond.hettinger | 2008-01-04 04:22:53 +0100 (Fri, 04 Jan 2008) | 10 lines Minor fix-ups to named tuples: * Make the _replace() method respect subclassing. * Using property() to make _fields read-only wasn't a good idea. It caused len(Point._fields) to fail. * Add note to _cast() about length checking and alternative with the star-operator. ........ r59707 | jeffrey.yasskin | 2008-01-04 09:01:23 +0100 (Fri, 04 Jan 2008) | 3 lines Make math.{floor,ceil}({int,long}) return float again for backwards compatibility after r59671 made them return integral types. ........ r59709 | christian.heimes | 2008-01-04 14:21:07 +0100 (Fri, 04 Jan 2008) | 1 line Bug #1713: posixpath.ismount() claims symlink to a mountpoint is a mountpoint. ........ r59712 | lars.gustaebel | 2008-01-04 15:00:33 +0100 (Fri, 04 Jan 2008) | 5 lines Issue #1735: TarFile.extractall() now correctly sets directory permissions and times. (will backport to 2.5) ........ r59714 | andrew.kuchling | 2008-01-04 15:47:17 +0100 (Fri, 04 Jan 2008) | 1 line Update links to bug/patch tracker ........ r59716 | christian.heimes | 2008-01-04 16:23:30 +0100 (Fri, 04 Jan 2008) | 1 line Added interface to Windows' WSAIoctl and a simple example for a network sniffer. ........ r59717 | christian.heimes | 2008-01-04 16:29:00 +0100 (Fri, 04 Jan 2008) | 1 line And here is the rest of Hirokazu Yamamoto's patch for VS6.0 support. Thanks Hiro! ........ r59719 | christian.heimes | 2008-01-04 16:34:06 +0100 (Fri, 04 Jan 2008) | 1 line Reverted last transaction. It's the wrong branch. ........ r59721 | christian.heimes | 2008-01-04 16:48:06 +0100 (Fri, 04 Jan 2008) | 1 line socket.ioctl is only available on Windows ........ r59722 | andrew.kuchling | 2008-01-04 19:24:41 +0100 (Fri, 04 Jan 2008) | 1 line Fix markup ........ r59723 | andrew.kuchling | 2008-01-04 19:25:05 +0100 (Fri, 04 Jan 2008) | 1 line Fix markup ........ r59725 | guido.van.rossum | 2008-01-05 01:59:59 +0100 (Sat, 05 Jan 2008) | 3 lines Patch #1725 by Mark Dickinson, fixes incorrect conversion of -1e1000 and adds errors for -0x. ........ r59726 | guido.van.rossum | 2008-01-05 02:21:57 +0100 (Sat, 05 Jan 2008) | 2 lines Patch #1698 by Senthil: allow '@' in username when parsed by urlparse.py. ........ r59727 | raymond.hettinger | 2008-01-05 02:35:43 +0100 (Sat, 05 Jan 2008) | 1 line Improve namedtuple's _cast() method with a docstring, new name, and error-checking. ........ r59728 | raymond.hettinger | 2008-01-05 03:17:24 +0100 (Sat, 05 Jan 2008) | 1 line Add error-checking to namedtuple's _replace() method. ........ r59730 | fred.drake | 2008-01-05 05:38:38 +0100 (Sat, 05 Jan 2008) | 2 lines clean up a comment ........ r59731 | jeffrey.yasskin | 2008-01-05 09:47:13 +0100 (Sat, 05 Jan 2008) | 11 lines Continue rolling back pep-3141 changes that changed behavior from 2.5. This round included: * Revert round to its 2.6 behavior (half away from 0). * Because round, floor, and ceil always return float again, it's no longer necessary to have them delegate to __xxx___, so I've ripped that out of their implementations and the Real ABC. This also helps in implementing types that work in both 2.6 and 3.0: you return int from the __xxx__ methods, and let it get enabled by the version upgrade. * Make pow(-1, .5) raise a ValueError again. ........ r59736 | andrew.kuchling | 2008-01-05 16:13:49 +0100 (Sat, 05 Jan 2008) | 1 line Fix comment typo ........ r59738 | thomas.heller | 2008-01-05 18:15:44 +0100 (Sat, 05 Jan 2008) | 1 line Add myself. ........ r59739 | georg.brandl | 2008-01-05 18:49:17 +0100 (Sat, 05 Jan 2008) | 2 lines Fix C++-style comment. ........ r59742 | georg.brandl | 2008-01-05 20:28:16 +0100 (Sat, 05 Jan 2008) | 2 lines Remove with_statement future imports from 2.6 docs. ........ r59743 | georg.brandl | 2008-01-05 20:29:45 +0100 (Sat, 05 Jan 2008) | 2 lines Simplify index entries; fix #1712. ........ r59744 | georg.brandl | 2008-01-05 20:44:22 +0100 (Sat, 05 Jan 2008) | 2 lines Doc patch #1730 from Robin Stocker; minor corrections mostly to os.rst. ........ r59749 | georg.brandl | 2008-01-05 21:29:13 +0100 (Sat, 05 Jan 2008) | 2 lines Revert socket.rst to unix-eol. ........ r59750 | georg.brandl | 2008-01-05 21:33:46 +0100 (Sat, 05 Jan 2008) | 2 lines Set native svn:eol-style property for text files. ........ r59752 | georg.brandl | 2008-01-05 21:46:29 +0100 (Sat, 05 Jan 2008) | 2 lines #1719: capitalization error in "UuidCreate". ........ r59753 | georg.brandl | 2008-01-05 22:02:25 +0100 (Sat, 05 Jan 2008) | 2 lines Repair markup. ........ r59754 | georg.brandl | 2008-01-05 22:10:50 +0100 (Sat, 05 Jan 2008) | 2 lines Use markup. ........ r59757 | christian.heimes | 2008-01-05 22:35:52 +0100 (Sat, 05 Jan 2008) | 1 line Final adjustments for #1601 ........ r59758 | guido.van.rossum | 2008-01-05 23:19:06 +0100 (Sat, 05 Jan 2008) | 3 lines Patch #1637: fix urlparse for URLs like 'http://x.com?arg=/foo'. Fix by John Nagle. ........ r59759 | guido.van.rossum | 2008-01-05 23:20:01 +0100 (Sat, 05 Jan 2008) | 2 lines Add John Nagle (of issue #1637). ........ r59765 | raymond.hettinger | 2008-01-06 10:02:24 +0100 (Sun, 06 Jan 2008) | 1 line Small code simplification. Forgot that classmethods can be called from intances. ........ r59766 | martin.v.loewis | 2008-01-06 11:09:48 +0100 (Sun, 06 Jan 2008) | 2 lines Use vcbuild for VS 2009. ........ r59767 | martin.v.loewis | 2008-01-06 12:03:43 +0100 (Sun, 06 Jan 2008) | 2 lines Package using VS 2008. ........ r59768 | martin.v.loewis | 2008-01-06 12:13:16 +0100 (Sun, 06 Jan 2008) | 2 lines Don't try to package msvcr90 for the moment. ........ r59769 | georg.brandl | 2008-01-06 15:17:36 +0100 (Sun, 06 Jan 2008) | 4 lines #1696393: don't check for '.' and '..' in ntpath.walk since they aren't returned from os.listdir anymore. Reported by Michael Haggerty. ........ r59770 | georg.brandl | 2008-01-06 15:27:15 +0100 (Sun, 06 Jan 2008) | 3 lines #1742: don't raise exception on os.path.relpath("a", "a"), but return os.curdir. Reported by Jesse Towner. ........ r59771 | georg.brandl | 2008-01-06 15:33:52 +0100 (Sun, 06 Jan 2008) | 2 lines #1591: Clarify docstring of Popen3. ........ r59772 | georg.brandl | 2008-01-06 16:30:34 +0100 (Sun, 06 Jan 2008) | 2 lines #1680: fix context manager example function name. ........ r59773 | georg.brandl | 2008-01-06 16:34:57 +0100 (Sun, 06 Jan 2008) | 2 lines #1755097: document default values for [].sort() and sorted(). ........
2008-01-06 12:59:19 -04:00
keyword: except
keyword: finally
keyword: else
keyword: as
single: : (colon); compound statement
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The :keyword:`!try` statement specifies exception handlers and/or cleanup code
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for a group of statements:
.. productionlist:: python-grammar
try_stmt: `try1_stmt` | `try2_stmt` | `try3_stmt`
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try1_stmt: "try" ":" `suite`
: ("except" [`expression` ["as" `identifier`]] ":" `suite`)+
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: ["else" ":" `suite`]
: ["finally" ":" `suite`]
try2_stmt: "try" ":" `suite`
: ("except" "*" `expression` ["as" `identifier`] ":" `suite`)+
: ["else" ":" `suite`]
: ["finally" ":" `suite`]
try3_stmt: "try" ":" `suite`
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: "finally" ":" `suite`
Additional information on exceptions can be found in section :ref:`exceptions`,
and information on using the :keyword:`raise` statement to generate exceptions
may be found in section :ref:`raise`.
Merged revisions 59703-59773 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r59704 | christian.heimes | 2008-01-04 04:15:05 +0100 (Fri, 04 Jan 2008) | 1 line Moved include "Python.h" in front of other imports to silence a warning. ........ r59706 | raymond.hettinger | 2008-01-04 04:22:53 +0100 (Fri, 04 Jan 2008) | 10 lines Minor fix-ups to named tuples: * Make the _replace() method respect subclassing. * Using property() to make _fields read-only wasn't a good idea. It caused len(Point._fields) to fail. * Add note to _cast() about length checking and alternative with the star-operator. ........ r59707 | jeffrey.yasskin | 2008-01-04 09:01:23 +0100 (Fri, 04 Jan 2008) | 3 lines Make math.{floor,ceil}({int,long}) return float again for backwards compatibility after r59671 made them return integral types. ........ r59709 | christian.heimes | 2008-01-04 14:21:07 +0100 (Fri, 04 Jan 2008) | 1 line Bug #1713: posixpath.ismount() claims symlink to a mountpoint is a mountpoint. ........ r59712 | lars.gustaebel | 2008-01-04 15:00:33 +0100 (Fri, 04 Jan 2008) | 5 lines Issue #1735: TarFile.extractall() now correctly sets directory permissions and times. (will backport to 2.5) ........ r59714 | andrew.kuchling | 2008-01-04 15:47:17 +0100 (Fri, 04 Jan 2008) | 1 line Update links to bug/patch tracker ........ r59716 | christian.heimes | 2008-01-04 16:23:30 +0100 (Fri, 04 Jan 2008) | 1 line Added interface to Windows' WSAIoctl and a simple example for a network sniffer. ........ r59717 | christian.heimes | 2008-01-04 16:29:00 +0100 (Fri, 04 Jan 2008) | 1 line And here is the rest of Hirokazu Yamamoto's patch for VS6.0 support. Thanks Hiro! ........ r59719 | christian.heimes | 2008-01-04 16:34:06 +0100 (Fri, 04 Jan 2008) | 1 line Reverted last transaction. It's the wrong branch. ........ r59721 | christian.heimes | 2008-01-04 16:48:06 +0100 (Fri, 04 Jan 2008) | 1 line socket.ioctl is only available on Windows ........ r59722 | andrew.kuchling | 2008-01-04 19:24:41 +0100 (Fri, 04 Jan 2008) | 1 line Fix markup ........ r59723 | andrew.kuchling | 2008-01-04 19:25:05 +0100 (Fri, 04 Jan 2008) | 1 line Fix markup ........ r59725 | guido.van.rossum | 2008-01-05 01:59:59 +0100 (Sat, 05 Jan 2008) | 3 lines Patch #1725 by Mark Dickinson, fixes incorrect conversion of -1e1000 and adds errors for -0x. ........ r59726 | guido.van.rossum | 2008-01-05 02:21:57 +0100 (Sat, 05 Jan 2008) | 2 lines Patch #1698 by Senthil: allow '@' in username when parsed by urlparse.py. ........ r59727 | raymond.hettinger | 2008-01-05 02:35:43 +0100 (Sat, 05 Jan 2008) | 1 line Improve namedtuple's _cast() method with a docstring, new name, and error-checking. ........ r59728 | raymond.hettinger | 2008-01-05 03:17:24 +0100 (Sat, 05 Jan 2008) | 1 line Add error-checking to namedtuple's _replace() method. ........ r59730 | fred.drake | 2008-01-05 05:38:38 +0100 (Sat, 05 Jan 2008) | 2 lines clean up a comment ........ r59731 | jeffrey.yasskin | 2008-01-05 09:47:13 +0100 (Sat, 05 Jan 2008) | 11 lines Continue rolling back pep-3141 changes that changed behavior from 2.5. This round included: * Revert round to its 2.6 behavior (half away from 0). * Because round, floor, and ceil always return float again, it's no longer necessary to have them delegate to __xxx___, so I've ripped that out of their implementations and the Real ABC. This also helps in implementing types that work in both 2.6 and 3.0: you return int from the __xxx__ methods, and let it get enabled by the version upgrade. * Make pow(-1, .5) raise a ValueError again. ........ r59736 | andrew.kuchling | 2008-01-05 16:13:49 +0100 (Sat, 05 Jan 2008) | 1 line Fix comment typo ........ r59738 | thomas.heller | 2008-01-05 18:15:44 +0100 (Sat, 05 Jan 2008) | 1 line Add myself. ........ r59739 | georg.brandl | 2008-01-05 18:49:17 +0100 (Sat, 05 Jan 2008) | 2 lines Fix C++-style comment. ........ r59742 | georg.brandl | 2008-01-05 20:28:16 +0100 (Sat, 05 Jan 2008) | 2 lines Remove with_statement future imports from 2.6 docs. ........ r59743 | georg.brandl | 2008-01-05 20:29:45 +0100 (Sat, 05 Jan 2008) | 2 lines Simplify index entries; fix #1712. ........ r59744 | georg.brandl | 2008-01-05 20:44:22 +0100 (Sat, 05 Jan 2008) | 2 lines Doc patch #1730 from Robin Stocker; minor corrections mostly to os.rst. ........ r59749 | georg.brandl | 2008-01-05 21:29:13 +0100 (Sat, 05 Jan 2008) | 2 lines Revert socket.rst to unix-eol. ........ r59750 | georg.brandl | 2008-01-05 21:33:46 +0100 (Sat, 05 Jan 2008) | 2 lines Set native svn:eol-style property for text files. ........ r59752 | georg.brandl | 2008-01-05 21:46:29 +0100 (Sat, 05 Jan 2008) | 2 lines #1719: capitalization error in "UuidCreate". ........ r59753 | georg.brandl | 2008-01-05 22:02:25 +0100 (Sat, 05 Jan 2008) | 2 lines Repair markup. ........ r59754 | georg.brandl | 2008-01-05 22:10:50 +0100 (Sat, 05 Jan 2008) | 2 lines Use markup. ........ r59757 | christian.heimes | 2008-01-05 22:35:52 +0100 (Sat, 05 Jan 2008) | 1 line Final adjustments for #1601 ........ r59758 | guido.van.rossum | 2008-01-05 23:19:06 +0100 (Sat, 05 Jan 2008) | 3 lines Patch #1637: fix urlparse for URLs like 'http://x.com?arg=/foo'. Fix by John Nagle. ........ r59759 | guido.van.rossum | 2008-01-05 23:20:01 +0100 (Sat, 05 Jan 2008) | 2 lines Add John Nagle (of issue #1637). ........ r59765 | raymond.hettinger | 2008-01-06 10:02:24 +0100 (Sun, 06 Jan 2008) | 1 line Small code simplification. Forgot that classmethods can be called from intances. ........ r59766 | martin.v.loewis | 2008-01-06 11:09:48 +0100 (Sun, 06 Jan 2008) | 2 lines Use vcbuild for VS 2009. ........ r59767 | martin.v.loewis | 2008-01-06 12:03:43 +0100 (Sun, 06 Jan 2008) | 2 lines Package using VS 2008. ........ r59768 | martin.v.loewis | 2008-01-06 12:13:16 +0100 (Sun, 06 Jan 2008) | 2 lines Don't try to package msvcr90 for the moment. ........ r59769 | georg.brandl | 2008-01-06 15:17:36 +0100 (Sun, 06 Jan 2008) | 4 lines #1696393: don't check for '.' and '..' in ntpath.walk since they aren't returned from os.listdir anymore. Reported by Michael Haggerty. ........ r59770 | georg.brandl | 2008-01-06 15:27:15 +0100 (Sun, 06 Jan 2008) | 3 lines #1742: don't raise exception on os.path.relpath("a", "a"), but return os.curdir. Reported by Jesse Towner. ........ r59771 | georg.brandl | 2008-01-06 15:33:52 +0100 (Sun, 06 Jan 2008) | 2 lines #1591: Clarify docstring of Popen3. ........ r59772 | georg.brandl | 2008-01-06 16:30:34 +0100 (Sun, 06 Jan 2008) | 2 lines #1680: fix context manager example function name. ........ r59773 | georg.brandl | 2008-01-06 16:34:57 +0100 (Sun, 06 Jan 2008) | 2 lines #1755097: document default values for [].sort() and sorted(). ........
2008-01-06 12:59:19 -04:00
.. _except:
:keyword:`!except` clause
-------------------------
The :keyword:`!except` clause(s) specify one or more exception handlers. When no
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exception occurs in the :keyword:`try` clause, no exception handler is executed.
When an exception occurs in the :keyword:`!try` suite, a search for an exception
handler is started. This search inspects the :keyword:`!except` clauses in turn
until one is found that matches the exception.
An expression-less :keyword:`!except` clause, if present, must be last;
it matches any exception.
For an :keyword:`!except` clause with an expression,
that expression is evaluated, and the clause matches the exception
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if the resulting object is "compatible" with the exception. An object is
compatible with an exception if the object is the class or a
:term:`non-virtual base class <abstract base class>` of the exception object,
or a tuple containing an item that is the class or a non-virtual base class
of the exception object.
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If no :keyword:`!except` clause matches the exception,
the search for an exception handler
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continues in the surrounding code and on the invocation stack. [#]_
If the evaluation of an expression
in the header of an :keyword:`!except` clause raises an exception,
the original search for a handler is canceled and a search starts for
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the new exception in the surrounding code and on the call stack (it is treated
as if the entire :keyword:`try` statement raised the exception).
.. index:: single: as; except clause
When a matching :keyword:`!except` clause is found,
the exception is assigned to the target
specified after the :keyword:`!as` keyword in that :keyword:`!except` clause,
if present, and the :keyword:`!except` clause's suite is executed.
All :keyword:`!except` clauses must have an executable block.
When the end of this block is reached, execution continues
normally after the entire :keyword:`try` statement.
(This means that if two nested handlers exist for the same exception,
and the exception occurs in the :keyword:`!try` clause of the inner handler,
the outer handler will not handle the exception.)
When an exception has been assigned using ``as target``, it is cleared at the
end of the :keyword:`!except` clause. This is as if ::
except E as N:
foo
was translated to ::
except E as N:
try:
foo
finally:
del N
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This means the exception must be assigned to a different name to be able to
refer to it after the :keyword:`!except` clause.
Exceptions are cleared because with the
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traceback attached to them, they form a reference cycle with the stack frame,
keeping all locals in that frame alive until the next garbage collection occurs.
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.. index::
module: sys
object: traceback
Before an :keyword:`!except` clause's suite is executed,
the exception is stored in the :mod:`sys` module, where it can be accessed
from within the body of the :keyword:`!except` clause by calling
:func:`sys.exception`. When leaving an exception handler, the exception
stored in the :mod:`sys` module is reset to its previous value::
>>> print(sys.exception())
None
>>> try:
... raise TypeError
... except:
... print(repr(sys.exception()))
... try:
... raise ValueError
... except:
... print(repr(sys.exception()))
... print(repr(sys.exception()))
...
TypeError()
ValueError()
TypeError()
>>> print(sys.exception())
None
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.. index::
keyword: except_star
.. _except_star:
:keyword:`!except*` clause
--------------------------
The :keyword:`!except*` clause(s) are used for handling
:exc:`ExceptionGroup`\s. The exception type for matching is interpreted as in
the case of :keyword:`except`, but in the case of exception groups we can have
partial matches when the type matches some of the exceptions in the group.
This means that multiple :keyword:`!except*` clauses can execute,
each handling part of the exception group.
Each clause executes at most once and handles an exception group
of all matching exceptions. Each exception in the group is handled by at most
one :keyword:`!except*` clause, the first that matches it. ::
>>> try:
... raise ExceptionGroup("eg",
... [ValueError(1), TypeError(2), OSError(3), OSError(4)])
... except* TypeError as e:
... print(f'caught {type(e)} with nested {e.exceptions}')
... except* OSError as e:
... print(f'caught {type(e)} with nested {e.exceptions}')
...
caught <class 'ExceptionGroup'> with nested (TypeError(2),)
caught <class 'ExceptionGroup'> with nested (OSError(3), OSError(4))
+ Exception Group Traceback (most recent call last):
| File "<stdin>", line 2, in <module>
| ExceptionGroup: eg
+-+---------------- 1 ----------------
| ValueError: 1
+------------------------------------
Any remaining exceptions that were not handled by any :keyword:`!except*`
clause are re-raised at the end, combined into an exception group along with
all exceptions that were raised from within :keyword:`!except*` clauses.
If the raised exception is not an exception group and its type matches
one of the :keyword:`!except*` clauses, it is caught and wrapped by an
exception group with an empty message string. ::
>>> try:
... raise BlockingIOError
... except* BlockingIOError as e:
... print(repr(e))
...
ExceptionGroup('', (BlockingIOError()))
An :keyword:`!except*` clause must have a matching type,
and this type cannot be a subclass of :exc:`BaseExceptionGroup`.
It is not possible to mix :keyword:`except` and :keyword:`!except*`
in the same :keyword:`try`.
:keyword:`break`, :keyword:`continue` and :keyword:`return`
cannot appear in an :keyword:`!except*` clause.
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.. index::
keyword: else
statement: return
statement: break
statement: continue
.. _except_else:
:keyword:`!else` clause
-----------------------
The optional :keyword:`!else` clause is executed if the control flow leaves the
:keyword:`try` suite, no exception was raised, and no :keyword:`return`,
:keyword:`continue`, or :keyword:`break` statement was executed. Exceptions in
the :keyword:`!else` clause are not handled by the preceding :keyword:`except`
clauses.
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.. index:: keyword: finally
.. _finally:
:keyword:`!finally` clause
--------------------------
If :keyword:`!finally` is present, it specifies a 'cleanup' handler. The
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:keyword:`try` clause is executed, including any :keyword:`except` and
:keyword:`else` clauses. If an exception occurs in any of the clauses and is
not handled, the exception is temporarily saved. The :keyword:`!finally` clause
is executed. If there is a saved exception it is re-raised at the end of the
:keyword:`!finally` clause. If the :keyword:`!finally` clause raises another
exception, the saved exception is set as the context of the new exception.
If the :keyword:`!finally` clause executes a :keyword:`return`, :keyword:`break`
or :keyword:`continue` statement, the saved exception is discarded::
>>> def f():
... try:
... 1/0
... finally:
... return 42
...
>>> f()
42
The exception information is not available to the program during execution of
the :keyword:`!finally` clause.
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.. index::
statement: return
statement: break
statement: continue
When a :keyword:`return`, :keyword:`break` or :keyword:`continue` statement is
executed in the :keyword:`try` suite of a :keyword:`!try`...\ :keyword:`!finally`
statement, the :keyword:`!finally` clause is also executed 'on the way out.'
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The return value of a function is determined by the last :keyword:`return`
statement executed. Since the :keyword:`!finally` clause always executes, a
:keyword:`!return` statement executed in the :keyword:`!finally` clause will
always be the last one executed::
>>> def foo():
... try:
... return 'try'
... finally:
... return 'finally'
...
>>> foo()
'finally'
.. versionchanged:: 3.8
Prior to Python 3.8, a :keyword:`continue` statement was illegal in the
:keyword:`!finally` clause due to a problem with the implementation.
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.. _with:
.. _as:
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The :keyword:`!with` statement
==============================
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.. index::
! statement: with
keyword: as
single: as; with statement
single: , (comma); with statement
single: : (colon); compound statement
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The :keyword:`with` statement is used to wrap the execution of a block with
methods defined by a context manager (see section :ref:`context-managers`).
This allows common :keyword:`try`...\ :keyword:`except`...\ :keyword:`finally`
usage patterns to be encapsulated for convenient reuse.
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.. productionlist:: python-grammar
with_stmt: "with" ( "(" `with_stmt_contents` ","? ")" | `with_stmt_contents` ) ":" `suite`
with_stmt_contents: `with_item` ("," `with_item`)*
with_item: `expression` ["as" `target`]
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The execution of the :keyword:`with` statement with one "item" proceeds as follows:
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#. The context expression (the expression given in the
:token:`~python-grammar:with_item`) is evaluated to obtain a context manager.
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#. The context manager's :meth:`__enter__` is loaded for later use.
#. The context manager's :meth:`__exit__` is loaded for later use.
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#. The context manager's :meth:`__enter__` method is invoked.
#. If a target was included in the :keyword:`with` statement, the return value
from :meth:`__enter__` is assigned to it.
.. note::
The :keyword:`with` statement guarantees that if the :meth:`__enter__`
method returns without an error, then :meth:`__exit__` will always be
called. Thus, if an error occurs during the assignment to the target list,
it will be treated the same as an error occurring within the suite would
be. See step 7 below.
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#. The suite is executed.
#. The context manager's :meth:`__exit__` method is invoked. If an exception
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caused the suite to be exited, its type, value, and traceback are passed as
arguments to :meth:`__exit__`. Otherwise, three :const:`None` arguments are
supplied.
If the suite was exited due to an exception, and the return value from the
:meth:`__exit__` method was false, the exception is reraised. If the return
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value was true, the exception is suppressed, and execution continues with the
statement following the :keyword:`with` statement.
If the suite was exited for any reason other than an exception, the return
value from :meth:`__exit__` is ignored, and execution proceeds at the normal
location for the kind of exit that was taken.
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The following code::
with EXPRESSION as TARGET:
SUITE
is semantically equivalent to::
manager = (EXPRESSION)
enter = type(manager).__enter__
exit = type(manager).__exit__
value = enter(manager)
hit_except = False
try:
TARGET = value
SUITE
except:
hit_except = True
if not exit(manager, *sys.exc_info()):
raise
finally:
if not hit_except:
exit(manager, None, None, None)
With more than one item, the context managers are processed as if multiple
:keyword:`with` statements were nested::
with A() as a, B() as b:
SUITE
is semantically equivalent to::
with A() as a:
with B() as b:
SUITE
You can also write multi-item context managers in multiple lines if
the items are surrounded by parentheses. For example::
with (
A() as a,
B() as b,
):
SUITE
.. versionchanged:: 3.1
Support for multiple context expressions.
.. versionchanged:: 3.10
Support for using grouping parentheses to break the statement in multiple lines.
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.. seealso::
:pep:`343` - The "with" statement
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The specification, background, and examples for the Python :keyword:`with`
statement.
.. _match:
The :keyword:`!match` statement
===============================
.. index::
! statement: match
! keyword: case
! single: pattern matching
keyword: if
keyword: as
pair: match; case
single: as; match statement
single: : (colon); compound statement
.. versionadded:: 3.10
The match statement is used for pattern matching. Syntax:
.. productionlist:: python-grammar
match_stmt: 'match' `subject_expr` ":" NEWLINE INDENT `case_block`+ DEDENT
subject_expr: `star_named_expression` "," `star_named_expressions`?
: | `named_expression`
case_block: 'case' `patterns` [`guard`] ":" `block`
.. note::
This section uses single quotes to denote
:ref:`soft keywords <soft-keywords>`.
Pattern matching takes a pattern as input (following ``case``) and a subject
value (following ``match``). The pattern (which may contain subpatterns) is
matched against the subject value. The outcomes are:
* A match success or failure (also termed a pattern success or failure).
* Possible binding of matched values to a name. The prerequisites for this are
further discussed below.
The ``match`` and ``case`` keywords are :ref:`soft keywords <soft-keywords>`.
.. seealso::
* :pep:`634` -- Structural Pattern Matching: Specification
* :pep:`636` -- Structural Pattern Matching: Tutorial
Overview
--------
Here's an overview of the logical flow of a match statement:
#. The subject expression ``subject_expr`` is evaluated and a resulting subject
value obtained. If the subject expression contains a comma, a tuple is
constructed using :ref:`the standard rules <typesseq-tuple>`.
#. Each pattern in a ``case_block`` is attempted to match with the subject value. The
specific rules for success or failure are described below. The match attempt can also
bind some or all of the standalone names within the pattern. The precise
pattern binding rules vary per pattern type and are
specified below. **Name bindings made during a successful pattern match
outlive the executed block and can be used after the match statement**.
.. note::
During failed pattern matches, some subpatterns may succeed. Do not
rely on bindings being made for a failed match. Conversely, do not
rely on variables remaining unchanged after a failed match. The exact
behavior is dependent on implementation and may vary. This is an
intentional decision made to allow different implementations to add
optimizations.
#. If the pattern succeeds, the corresponding guard (if present) is evaluated. In
this case all name bindings are guaranteed to have happened.
* If the guard evaluates as true or is missing, the ``block`` inside
``case_block`` is executed.
* Otherwise, the next ``case_block`` is attempted as described above.
* If there are no further case blocks, the match statement is completed.
.. note::
Users should generally never rely on a pattern being evaluated. Depending on
implementation, the interpreter may cache values or use other optimizations
which skip repeated evaluations.
A sample match statement::
>>> flag = False
>>> match (100, 200):
... case (100, 300): # Mismatch: 200 != 300
... print('Case 1')
... case (100, 200) if flag: # Successful match, but guard fails
... print('Case 2')
... case (100, y): # Matches and binds y to 200
... print(f'Case 3, y: {y}')
... case _: # Pattern not attempted
... print('Case 4, I match anything!')
...
Case 3, y: 200
In this case, ``if flag`` is a guard. Read more about that in the next section.
Guards
------
.. index:: ! guard
.. productionlist:: python-grammar
guard: "if" `named_expression`
A ``guard`` (which is part of the ``case``) must succeed for code inside
the ``case`` block to execute. It takes the form: :keyword:`if` followed by an
expression.
The logical flow of a ``case`` block with a ``guard`` follows:
#. Check that the pattern in the ``case`` block succeeded. If the pattern
failed, the ``guard`` is not evaluated and the next ``case`` block is
checked.
#. If the pattern succeeded, evaluate the ``guard``.
* If the ``guard`` condition evaluates as true, the case block is
selected.
* If the ``guard`` condition evaluates as false, the case block is not
selected.
* If the ``guard`` raises an exception during evaluation, the exception
bubbles up.
Guards are allowed to have side effects as they are expressions. Guard
evaluation must proceed from the first to the last case block, one at a time,
skipping case blocks whose pattern(s) don't all succeed. (I.e.,
guard evaluation must happen in order.) Guard evaluation must stop once a case
block is selected.
.. _irrefutable_case:
Irrefutable Case Blocks
-----------------------
.. index:: irrefutable case block, case block
An irrefutable case block is a match-all case block. A match statement may have
at most one irrefutable case block, and it must be last.
A case block is considered irrefutable if it has no guard and its pattern is
irrefutable. A pattern is considered irrefutable if we can prove from its
syntax alone that it will always succeed. Only the following patterns are
irrefutable:
* :ref:`as-patterns` whose left-hand side is irrefutable
* :ref:`or-patterns` containing at least one irrefutable pattern
* :ref:`capture-patterns`
* :ref:`wildcard-patterns`
* parenthesized irrefutable patterns
Patterns
--------
.. index::
single: ! patterns
single: AS pattern, OR pattern, capture pattern, wildcard pattern
.. note::
This section uses grammar notations beyond standard EBNF:
* the notation ``SEP.RULE+`` is shorthand for ``RULE (SEP RULE)*``
* the notation ``!RULE`` is shorthand for a negative lookahead assertion
The top-level syntax for ``patterns`` is:
.. productionlist:: python-grammar
patterns: `open_sequence_pattern` | `pattern`
pattern: `as_pattern` | `or_pattern`
closed_pattern: | `literal_pattern`
: | `capture_pattern`
: | `wildcard_pattern`
: | `value_pattern`
: | `group_pattern`
: | `sequence_pattern`
: | `mapping_pattern`
: | `class_pattern`
The descriptions below will include a description "in simple terms" of what a pattern
does for illustration purposes (credits to Raymond Hettinger for a document that
inspired most of the descriptions). Note that these descriptions are purely for
illustration purposes and **may not** reflect
the underlying implementation. Furthermore, they do not cover all valid forms.
.. _or-patterns:
OR Patterns
^^^^^^^^^^^
An OR pattern is two or more patterns separated by vertical
bars ``|``. Syntax:
.. productionlist:: python-grammar
or_pattern: "|".`closed_pattern`+
Only the final subpattern may be :ref:`irrefutable <irrefutable_case>`, and each
subpattern must bind the same set of names to avoid ambiguity.
An OR pattern matches each of its subpatterns in turn to the subject value,
until one succeeds. The OR pattern is then considered successful. Otherwise,
if none of the subpatterns succeed, the OR pattern fails.
In simple terms, ``P1 | P2 | ...`` will try to match ``P1``, if it fails it will try to
match ``P2``, succeeding immediately if any succeeds, failing otherwise.
.. _as-patterns:
AS Patterns
^^^^^^^^^^^
An AS pattern matches an OR pattern on the left of the :keyword:`as`
keyword against a subject. Syntax:
.. productionlist:: python-grammar
as_pattern: `or_pattern` "as" `capture_pattern`
If the OR pattern fails, the AS pattern fails. Otherwise, the AS pattern binds
the subject to the name on the right of the as keyword and succeeds.
``capture_pattern`` cannot be a ``_``.
In simple terms ``P as NAME`` will match with ``P``, and on success it will
set ``NAME = <subject>``.
.. _literal-patterns:
Literal Patterns
^^^^^^^^^^^^^^^^
A literal pattern corresponds to most
:ref:`literals <literals>` in Python. Syntax:
.. productionlist:: python-grammar
literal_pattern: `signed_number`
: | `signed_number` "+" NUMBER
: | `signed_number` "-" NUMBER
: | `strings`
: | "None"
: | "True"
: | "False"
: | `signed_number`: NUMBER | "-" NUMBER
The rule ``strings`` and the token ``NUMBER`` are defined in the
:doc:`standard Python grammar <./grammar>`. Triple-quoted strings are
supported. Raw strings and byte strings are supported. :ref:`f-strings` are
not supported.
The forms ``signed_number '+' NUMBER`` and ``signed_number '-' NUMBER`` are
for expressing :ref:`complex numbers <imaginary>`; they require a real number
on the left and an imaginary number on the right. E.g. ``3 + 4j``.
In simple terms, ``LITERAL`` will succeed only if ``<subject> == LITERAL``. For
the singletons ``None``, ``True`` and ``False``, the :keyword:`is` operator is used.
.. _capture-patterns:
Capture Patterns
^^^^^^^^^^^^^^^^
A capture pattern binds the subject value to a name.
Syntax:
.. productionlist:: python-grammar
capture_pattern: !'_' NAME
A single underscore ``_`` is not a capture pattern (this is what ``!'_'``
expresses). It is instead treated as a
:token:`~python-grammar:wildcard_pattern`.
In a given pattern, a given name can only be bound once. E.g.
``case x, x: ...`` is invalid while ``case [x] | x: ...`` is allowed.
Capture patterns always succeed. The binding follows scoping rules
established by the assignment expression operator in :pep:`572`; the
name becomes a local variable in the closest containing function scope unless
there's an applicable :keyword:`global` or :keyword:`nonlocal` statement.
In simple terms ``NAME`` will always succeed and it will set ``NAME = <subject>``.
.. _wildcard-patterns:
Wildcard Patterns
^^^^^^^^^^^^^^^^^
A wildcard pattern always succeeds (matches anything)
and binds no name. Syntax:
.. productionlist:: python-grammar
wildcard_pattern: '_'
``_`` is a :ref:`soft keyword <soft-keywords>` within any pattern,
but only within patterns. It is an identifier, as usual, even within
``match`` subject expressions, ``guard``\ s, and ``case`` blocks.
In simple terms, ``_`` will always succeed.
.. _value-patterns:
Value Patterns
^^^^^^^^^^^^^^
A value pattern represents a named value in Python.
Syntax:
.. productionlist:: python-grammar
value_pattern: `attr`
attr: `name_or_attr` "." NAME
name_or_attr: `attr` | NAME
The dotted name in the pattern is looked up using standard Python
:ref:`name resolution rules <resolve_names>`. The pattern succeeds if the
value found compares equal to the subject value (using the ``==`` equality
operator).
In simple terms ``NAME1.NAME2`` will succeed only if ``<subject> == NAME1.NAME2``
.. note::
If the same value occurs multiple times in the same match statement, the
interpreter may cache the first value found and reuse it rather than repeat
the same lookup. This cache is strictly tied to a given execution of a
given match statement.
.. _group-patterns:
Group Patterns
^^^^^^^^^^^^^^
A group pattern allows users to add parentheses around patterns to
emphasize the intended grouping. Otherwise, it has no additional syntax.
Syntax:
.. productionlist:: python-grammar
group_pattern: "(" `pattern` ")"
In simple terms ``(P)`` has the same effect as ``P``.
.. _sequence-patterns:
Sequence Patterns
^^^^^^^^^^^^^^^^^
A sequence pattern contains several subpatterns to be matched against sequence elements.
The syntax is similar to the unpacking of a list or tuple.
.. productionlist:: python-grammar
sequence_pattern: "[" [`maybe_sequence_pattern`] "]"
: | "(" [`open_sequence_pattern`] ")"
open_sequence_pattern: `maybe_star_pattern` "," [`maybe_sequence_pattern`]
maybe_sequence_pattern: ",".`maybe_star_pattern`+ ","?
maybe_star_pattern: `star_pattern` | `pattern`
star_pattern: "*" (`capture_pattern` | `wildcard_pattern`)
There is no difference if parentheses or square brackets
are used for sequence patterns (i.e. ``(...)`` vs ``[...]`` ).
.. note::
A single pattern enclosed in parentheses without a trailing comma
(e.g. ``(3 | 4)``) is a :ref:`group pattern <group-patterns>`.
While a single pattern enclosed in square brackets (e.g. ``[3 | 4]``) is
still a sequence pattern.
At most one star subpattern may be in a sequence pattern. The star subpattern
may occur in any position. If no star subpattern is present, the sequence
pattern is a fixed-length sequence pattern; otherwise it is a variable-length
sequence pattern.
The following is the logical flow for matching a sequence pattern against a
subject value:
#. If the subject value is not a sequence [#]_, the sequence pattern
fails.
#. If the subject value is an instance of ``str``, ``bytes`` or ``bytearray``
the sequence pattern fails.
#. The subsequent steps depend on whether the sequence pattern is fixed or
variable-length.
If the sequence pattern is fixed-length:
#. If the length of the subject sequence is not equal to the number of
subpatterns, the sequence pattern fails
#. Subpatterns in the sequence pattern are matched to their corresponding
items in the subject sequence from left to right. Matching stops as soon
as a subpattern fails. If all subpatterns succeed in matching their
corresponding item, the sequence pattern succeeds.
Otherwise, if the sequence pattern is variable-length:
#. If the length of the subject sequence is less than the number of non-star
subpatterns, the sequence pattern fails.
#. The leading non-star subpatterns are matched to their corresponding items
as for fixed-length sequences.
#. If the previous step succeeds, the star subpattern matches a list formed
of the remaining subject items, excluding the remaining items
corresponding to non-star subpatterns following the star subpattern.
#. Remaining non-star subpatterns are matched to their corresponding subject
items, as for a fixed-length sequence.
.. note:: The length of the subject sequence is obtained via
:func:`len` (i.e. via the :meth:`__len__` protocol). This length may be
cached by the interpreter in a similar manner as
:ref:`value patterns <value-patterns>`.
In simple terms ``[P1, P2, P3,`` ... ``, P<N>]`` matches only if all the following
happens:
* check ``<subject>`` is a sequence
* ``len(subject) == <N>``
* ``P1`` matches ``<subject>[0]`` (note that this match can also bind names)
* ``P2`` matches ``<subject>[1]`` (note that this match can also bind names)
* ... and so on for the corresponding pattern/element.
.. _mapping-patterns:
Mapping Patterns
^^^^^^^^^^^^^^^^
A mapping pattern contains one or more key-value patterns. The syntax is
similar to the construction of a dictionary.
Syntax:
.. productionlist:: python-grammar
mapping_pattern: "{" [`items_pattern`] "}"
items_pattern: ",".`key_value_pattern`+ ","?
key_value_pattern: (`literal_pattern` | `value_pattern`) ":" `pattern`
: | `double_star_pattern`
double_star_pattern: "**" `capture_pattern`
At most one double star pattern may be in a mapping pattern. The double star
pattern must be the last subpattern in the mapping pattern.
Duplicate keys in mapping patterns are disallowed. Duplicate literal keys will
raise a :exc:`SyntaxError`. Two keys that otherwise have the same value will
raise a :exc:`ValueError` at runtime.
The following is the logical flow for matching a mapping pattern against a
subject value:
#. If the subject value is not a mapping [#]_,the mapping pattern fails.
#. If every key given in the mapping pattern is present in the subject mapping,
and the pattern for each key matches the corresponding item of the subject
mapping, the mapping pattern succeeds.
#. If duplicate keys are detected in the mapping pattern, the pattern is
considered invalid. A :exc:`SyntaxError` is raised for duplicate literal
values; or a :exc:`ValueError` for named keys of the same value.
.. note:: Key-value pairs are matched using the two-argument form of the mapping
subject's ``get()`` method. Matched key-value pairs must already be present
in the mapping, and not created on-the-fly via :meth:`__missing__` or
:meth:`__getitem__`.
In simple terms ``{KEY1: P1, KEY2: P2, ... }`` matches only if all the following
happens:
* check ``<subject>`` is a mapping
* ``KEY1 in <subject>``
* ``P1`` matches ``<subject>[KEY1]``
* ... and so on for the corresponding KEY/pattern pair.
.. _class-patterns:
Class Patterns
^^^^^^^^^^^^^^
A class pattern represents a class and its positional and keyword arguments
(if any). Syntax:
.. productionlist:: python-grammar
class_pattern: `name_or_attr` "(" [`pattern_arguments` ","?] ")"
pattern_arguments: `positional_patterns` ["," `keyword_patterns`]
: | `keyword_patterns`
positional_patterns: ",".`pattern`+
keyword_patterns: ",".`keyword_pattern`+
keyword_pattern: NAME "=" `pattern`
The same keyword should not be repeated in class patterns.
The following is the logical flow for matching a class pattern against a
subject value:
#. If ``name_or_attr`` is not an instance of the builtin :class:`type` , raise
:exc:`TypeError`.
#. If the subject value is not an instance of ``name_or_attr`` (tested via
:func:`isinstance`), the class pattern fails.
#. If no pattern arguments are present, the pattern succeeds. Otherwise,
the subsequent steps depend on whether keyword or positional argument patterns
are present.
For a number of built-in types (specified below), a single positional
subpattern is accepted which will match the entire subject; for these types
keyword patterns also work as for other types.
If only keyword patterns are present, they are processed as follows,
one by one:
I. The keyword is looked up as an attribute on the subject.
* If this raises an exception other than :exc:`AttributeError`, the
exception bubbles up.
* If this raises :exc:`AttributeError`, the class pattern has failed.
* Else, the subpattern associated with the keyword pattern is matched
against the subject's attribute value. If this fails, the class
pattern fails; if this succeeds, the match proceeds to the next keyword.
II. If all keyword patterns succeed, the class pattern succeeds.
If any positional patterns are present, they are converted to keyword
patterns using the :data:`~object.__match_args__` attribute on the class
``name_or_attr`` before matching:
I. The equivalent of ``getattr(cls, "__match_args__", ())`` is called.
* If this raises an exception, the exception bubbles up.
* If the returned value is not a tuple, the conversion fails and
:exc:`TypeError` is raised.
* If there are more positional patterns than ``len(cls.__match_args__)``,
:exc:`TypeError` is raised.
* Otherwise, positional pattern ``i`` is converted to a keyword pattern
using ``__match_args__[i]`` as the keyword. ``__match_args__[i]`` must
be a string; if not :exc:`TypeError` is raised.
* If there are duplicate keywords, :exc:`TypeError` is raised.
.. seealso:: :ref:`class-pattern-matching`
II. Once all positional patterns have been converted to keyword patterns,
the match proceeds as if there were only keyword patterns.
For the following built-in types the handling of positional subpatterns is
different:
* :class:`bool`
* :class:`bytearray`
* :class:`bytes`
* :class:`dict`
* :class:`float`
* :class:`frozenset`
* :class:`int`
* :class:`list`
* :class:`set`
* :class:`str`
* :class:`tuple`
These classes accept a single positional argument, and the pattern there is matched
against the whole object rather than an attribute. For example ``int(0|1)`` matches
the value ``0``, but not the value ``0.0``.
In simple terms ``CLS(P1, attr=P2)`` matches only if the following happens:
* ``isinstance(<subject>, CLS)``
* convert ``P1`` to a keyword pattern using ``CLS.__match_args__``
* For each keyword argument ``attr=P2``:
* ``hasattr(<subject>, "attr")``
* ``P2`` matches ``<subject>.attr``
* ... and so on for the corresponding keyword argument/pattern pair.
.. seealso::
* :pep:`634` -- Structural Pattern Matching: Specification
* :pep:`636` -- Structural Pattern Matching: Tutorial
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.. index::
single: parameter; function definition
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.. _function:
.. _def:
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Function definitions
====================
.. index::
statement: def
Merged revisions 59703-59773 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r59704 | christian.heimes | 2008-01-04 04:15:05 +0100 (Fri, 04 Jan 2008) | 1 line Moved include "Python.h" in front of other imports to silence a warning. ........ r59706 | raymond.hettinger | 2008-01-04 04:22:53 +0100 (Fri, 04 Jan 2008) | 10 lines Minor fix-ups to named tuples: * Make the _replace() method respect subclassing. * Using property() to make _fields read-only wasn't a good idea. It caused len(Point._fields) to fail. * Add note to _cast() about length checking and alternative with the star-operator. ........ r59707 | jeffrey.yasskin | 2008-01-04 09:01:23 +0100 (Fri, 04 Jan 2008) | 3 lines Make math.{floor,ceil}({int,long}) return float again for backwards compatibility after r59671 made them return integral types. ........ r59709 | christian.heimes | 2008-01-04 14:21:07 +0100 (Fri, 04 Jan 2008) | 1 line Bug #1713: posixpath.ismount() claims symlink to a mountpoint is a mountpoint. ........ r59712 | lars.gustaebel | 2008-01-04 15:00:33 +0100 (Fri, 04 Jan 2008) | 5 lines Issue #1735: TarFile.extractall() now correctly sets directory permissions and times. (will backport to 2.5) ........ r59714 | andrew.kuchling | 2008-01-04 15:47:17 +0100 (Fri, 04 Jan 2008) | 1 line Update links to bug/patch tracker ........ r59716 | christian.heimes | 2008-01-04 16:23:30 +0100 (Fri, 04 Jan 2008) | 1 line Added interface to Windows' WSAIoctl and a simple example for a network sniffer. ........ r59717 | christian.heimes | 2008-01-04 16:29:00 +0100 (Fri, 04 Jan 2008) | 1 line And here is the rest of Hirokazu Yamamoto's patch for VS6.0 support. Thanks Hiro! ........ r59719 | christian.heimes | 2008-01-04 16:34:06 +0100 (Fri, 04 Jan 2008) | 1 line Reverted last transaction. It's the wrong branch. ........ r59721 | christian.heimes | 2008-01-04 16:48:06 +0100 (Fri, 04 Jan 2008) | 1 line socket.ioctl is only available on Windows ........ r59722 | andrew.kuchling | 2008-01-04 19:24:41 +0100 (Fri, 04 Jan 2008) | 1 line Fix markup ........ r59723 | andrew.kuchling | 2008-01-04 19:25:05 +0100 (Fri, 04 Jan 2008) | 1 line Fix markup ........ r59725 | guido.van.rossum | 2008-01-05 01:59:59 +0100 (Sat, 05 Jan 2008) | 3 lines Patch #1725 by Mark Dickinson, fixes incorrect conversion of -1e1000 and adds errors for -0x. ........ r59726 | guido.van.rossum | 2008-01-05 02:21:57 +0100 (Sat, 05 Jan 2008) | 2 lines Patch #1698 by Senthil: allow '@' in username when parsed by urlparse.py. ........ r59727 | raymond.hettinger | 2008-01-05 02:35:43 +0100 (Sat, 05 Jan 2008) | 1 line Improve namedtuple's _cast() method with a docstring, new name, and error-checking. ........ r59728 | raymond.hettinger | 2008-01-05 03:17:24 +0100 (Sat, 05 Jan 2008) | 1 line Add error-checking to namedtuple's _replace() method. ........ r59730 | fred.drake | 2008-01-05 05:38:38 +0100 (Sat, 05 Jan 2008) | 2 lines clean up a comment ........ r59731 | jeffrey.yasskin | 2008-01-05 09:47:13 +0100 (Sat, 05 Jan 2008) | 11 lines Continue rolling back pep-3141 changes that changed behavior from 2.5. This round included: * Revert round to its 2.6 behavior (half away from 0). * Because round, floor, and ceil always return float again, it's no longer necessary to have them delegate to __xxx___, so I've ripped that out of their implementations and the Real ABC. This also helps in implementing types that work in both 2.6 and 3.0: you return int from the __xxx__ methods, and let it get enabled by the version upgrade. * Make pow(-1, .5) raise a ValueError again. ........ r59736 | andrew.kuchling | 2008-01-05 16:13:49 +0100 (Sat, 05 Jan 2008) | 1 line Fix comment typo ........ r59738 | thomas.heller | 2008-01-05 18:15:44 +0100 (Sat, 05 Jan 2008) | 1 line Add myself. ........ r59739 | georg.brandl | 2008-01-05 18:49:17 +0100 (Sat, 05 Jan 2008) | 2 lines Fix C++-style comment. ........ r59742 | georg.brandl | 2008-01-05 20:28:16 +0100 (Sat, 05 Jan 2008) | 2 lines Remove with_statement future imports from 2.6 docs. ........ r59743 | georg.brandl | 2008-01-05 20:29:45 +0100 (Sat, 05 Jan 2008) | 2 lines Simplify index entries; fix #1712. ........ r59744 | georg.brandl | 2008-01-05 20:44:22 +0100 (Sat, 05 Jan 2008) | 2 lines Doc patch #1730 from Robin Stocker; minor corrections mostly to os.rst. ........ r59749 | georg.brandl | 2008-01-05 21:29:13 +0100 (Sat, 05 Jan 2008) | 2 lines Revert socket.rst to unix-eol. ........ r59750 | georg.brandl | 2008-01-05 21:33:46 +0100 (Sat, 05 Jan 2008) | 2 lines Set native svn:eol-style property for text files. ........ r59752 | georg.brandl | 2008-01-05 21:46:29 +0100 (Sat, 05 Jan 2008) | 2 lines #1719: capitalization error in "UuidCreate". ........ r59753 | georg.brandl | 2008-01-05 22:02:25 +0100 (Sat, 05 Jan 2008) | 2 lines Repair markup. ........ r59754 | georg.brandl | 2008-01-05 22:10:50 +0100 (Sat, 05 Jan 2008) | 2 lines Use markup. ........ r59757 | christian.heimes | 2008-01-05 22:35:52 +0100 (Sat, 05 Jan 2008) | 1 line Final adjustments for #1601 ........ r59758 | guido.van.rossum | 2008-01-05 23:19:06 +0100 (Sat, 05 Jan 2008) | 3 lines Patch #1637: fix urlparse for URLs like 'http://x.com?arg=/foo'. Fix by John Nagle. ........ r59759 | guido.van.rossum | 2008-01-05 23:20:01 +0100 (Sat, 05 Jan 2008) | 2 lines Add John Nagle (of issue #1637). ........ r59765 | raymond.hettinger | 2008-01-06 10:02:24 +0100 (Sun, 06 Jan 2008) | 1 line Small code simplification. Forgot that classmethods can be called from intances. ........ r59766 | martin.v.loewis | 2008-01-06 11:09:48 +0100 (Sun, 06 Jan 2008) | 2 lines Use vcbuild for VS 2009. ........ r59767 | martin.v.loewis | 2008-01-06 12:03:43 +0100 (Sun, 06 Jan 2008) | 2 lines Package using VS 2008. ........ r59768 | martin.v.loewis | 2008-01-06 12:13:16 +0100 (Sun, 06 Jan 2008) | 2 lines Don't try to package msvcr90 for the moment. ........ r59769 | georg.brandl | 2008-01-06 15:17:36 +0100 (Sun, 06 Jan 2008) | 4 lines #1696393: don't check for '.' and '..' in ntpath.walk since they aren't returned from os.listdir anymore. Reported by Michael Haggerty. ........ r59770 | georg.brandl | 2008-01-06 15:27:15 +0100 (Sun, 06 Jan 2008) | 3 lines #1742: don't raise exception on os.path.relpath("a", "a"), but return os.curdir. Reported by Jesse Towner. ........ r59771 | georg.brandl | 2008-01-06 15:33:52 +0100 (Sun, 06 Jan 2008) | 2 lines #1591: Clarify docstring of Popen3. ........ r59772 | georg.brandl | 2008-01-06 16:30:34 +0100 (Sun, 06 Jan 2008) | 2 lines #1680: fix context manager example function name. ........ r59773 | georg.brandl | 2008-01-06 16:34:57 +0100 (Sun, 06 Jan 2008) | 2 lines #1755097: document default values for [].sort() and sorted(). ........
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pair: function; definition
pair: function; name
pair: name; binding
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object: user-defined function
object: function
pair: function; name
pair: name; binding
single: () (parentheses); function definition
single: , (comma); parameter list
single: : (colon); compound statement
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A function definition defines a user-defined function object (see section
:ref:`types`):
.. productionlist:: python-grammar
funcdef: [`decorators`] "def" `funcname` "(" [`parameter_list`] ")"
: ["->" `expression`] ":" `suite`
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decorators: `decorator`+
decorator: "@" `assignment_expression` NEWLINE
2019-05-29 18:59:00 -03:00
parameter_list: `defparameter` ("," `defparameter`)* "," "/" ["," [`parameter_list_no_posonly`]]
: | `parameter_list_no_posonly`
parameter_list_no_posonly: `defparameter` ("," `defparameter`)* ["," [`parameter_list_starargs`]]
: | `parameter_list_starargs`
parameter_list_starargs: "*" [`parameter`] ("," `defparameter`)* ["," ["**" `parameter` [","]]]
: | "**" `parameter` [","]
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parameter: `identifier` [":" `expression`]
defparameter: `parameter` ["=" `expression`]
funcname: `identifier`
A function definition is an executable statement. Its execution binds the
function name in the current local namespace to a function object (a wrapper
around the executable code for the function). This function object contains a
reference to the current global namespace as the global namespace to be used
when the function is called.
The function definition does not execute the function body; this gets executed
Merged revisions 65012,65035,65037-65040,65048,65057,65077,65091-65095,65097-65099,65127-65128,65131,65133-65136,65139,65149-65151,65155,65158-65159,65176-65178,65183-65184,65187-65190,65192,65194 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r65012 | jesse.noller | 2008-07-16 15:24:06 +0200 (Wed, 16 Jul 2008) | 2 lines Apply patch for issue 3090: ARCHFLAGS parsing incorrect ........ r65035 | georg.brandl | 2008-07-16 23:19:28 +0200 (Wed, 16 Jul 2008) | 2 lines #3045: fix pydoc behavior for TEMP path with spaces. ........ r65037 | georg.brandl | 2008-07-16 23:31:41 +0200 (Wed, 16 Jul 2008) | 2 lines #1608818: errno can get set by every call to readdir(). ........ r65038 | georg.brandl | 2008-07-17 00:04:20 +0200 (Thu, 17 Jul 2008) | 2 lines #3305: self->stream can be NULL. ........ r65039 | georg.brandl | 2008-07-17 00:09:17 +0200 (Thu, 17 Jul 2008) | 2 lines #3345: fix docstring. ........ r65040 | georg.brandl | 2008-07-17 00:33:18 +0200 (Thu, 17 Jul 2008) | 2 lines #3312: fix two sqlite3 crashes. ........ r65048 | georg.brandl | 2008-07-17 01:35:54 +0200 (Thu, 17 Jul 2008) | 2 lines #3388: add a paragraph about using "with" for file objects. ........ r65057 | gregory.p.smith | 2008-07-17 05:13:05 +0200 (Thu, 17 Jul 2008) | 2 lines news note for r63052 ........ r65077 | jesse.noller | 2008-07-17 23:01:05 +0200 (Thu, 17 Jul 2008) | 3 lines Fix issue 3395, update _debugInfo to be _debug_info ........ r65091 | ronald.oussoren | 2008-07-18 07:48:03 +0200 (Fri, 18 Jul 2008) | 2 lines Last bit of a fix for issue3381 (addon for my patch in r65061) ........ r65092 | vinay.sajip | 2008-07-18 10:59:06 +0200 (Fri, 18 Jul 2008) | 1 line Issue #3389: Allow resolving dotted names for handlers in logging configuration files. Thanks to Philip Jenvey for the patch. ........ r65093 | vinay.sajip | 2008-07-18 11:00:00 +0200 (Fri, 18 Jul 2008) | 1 line Issue #3389: Allow resolving dotted names for handlers in logging configuration files. Thanks to Philip Jenvey for the patch. ........ r65094 | vinay.sajip | 2008-07-18 11:00:35 +0200 (Fri, 18 Jul 2008) | 1 line Issue #3389: Allow resolving dotted names for handlers in logging configuration files. Thanks to Philip Jenvey for the patch. ........ r65095 | vinay.sajip | 2008-07-18 11:01:10 +0200 (Fri, 18 Jul 2008) | 1 line Issue #3389: Allow resolving dotted names for handlers in logging configuration files. Thanks to Philip Jenvey for the patch. ........ r65097 | georg.brandl | 2008-07-18 12:20:59 +0200 (Fri, 18 Jul 2008) | 2 lines Remove duplicate entry in __all__. ........ r65098 | georg.brandl | 2008-07-18 12:29:30 +0200 (Fri, 18 Jul 2008) | 2 lines Correct attribute name. ........ r65099 | georg.brandl | 2008-07-18 13:15:06 +0200 (Fri, 18 Jul 2008) | 3 lines Document the different meaning of precision for {:f} and {:g}. Also document how inf and nan are formatted. #3404. ........ r65127 | raymond.hettinger | 2008-07-19 02:42:03 +0200 (Sat, 19 Jul 2008) | 1 line Improve accuracy of gamma test function ........ r65128 | raymond.hettinger | 2008-07-19 02:43:00 +0200 (Sat, 19 Jul 2008) | 1 line Add recipe to the itertools docs. ........ r65131 | georg.brandl | 2008-07-19 12:08:55 +0200 (Sat, 19 Jul 2008) | 2 lines #3378: in case of no memory, don't leak even more memory. :) ........ r65133 | georg.brandl | 2008-07-19 14:39:10 +0200 (Sat, 19 Jul 2008) | 3 lines #3302: fix segfaults when passing None for arguments that can't be NULL for the C functions. ........ r65134 | georg.brandl | 2008-07-19 14:46:12 +0200 (Sat, 19 Jul 2008) | 2 lines #3303: fix crash with invalid Py_DECREF in strcoll(). ........ r65135 | georg.brandl | 2008-07-19 15:00:22 +0200 (Sat, 19 Jul 2008) | 3 lines #3319: don't raise ZeroDivisionError if number of rounds is so low that benchtime is zero. ........ r65136 | georg.brandl | 2008-07-19 15:09:42 +0200 (Sat, 19 Jul 2008) | 3 lines #3323: mention that if inheriting from a class without __slots__, the subclass will have a __dict__ available too. ........ r65139 | georg.brandl | 2008-07-19 15:48:44 +0200 (Sat, 19 Jul 2008) | 2 lines Add ordering info for findall and finditer. ........ r65149 | raymond.hettinger | 2008-07-20 01:21:57 +0200 (Sun, 20 Jul 2008) | 1 line Fix compress() recipe in docs to use itertools. ........ r65150 | raymond.hettinger | 2008-07-20 01:58:47 +0200 (Sun, 20 Jul 2008) | 1 line Clean-up itertools docs and recipes. ........ r65151 | gregory.p.smith | 2008-07-20 02:22:08 +0200 (Sun, 20 Jul 2008) | 9 lines fix issue3120 - don't truncate handles on 64-bit Windows. This is still messy, realistically PC/_subprocess.c should never cast pointers to python numbers and back at all. I don't have a 64-bit windows build environment because microsoft apparently thinks that should cost money. Time to watch the buildbots. It builds and passes tests on 32-bit windows. ........ r65155 | georg.brandl | 2008-07-20 13:50:29 +0200 (Sun, 20 Jul 2008) | 2 lines #926501: add info where to put the docstring. ........ r65158 | neal.norwitz | 2008-07-20 21:35:23 +0200 (Sun, 20 Jul 2008) | 1 line Fix a couple of names in error messages that were wrong ........ r65159 | neal.norwitz | 2008-07-20 22:39:36 +0200 (Sun, 20 Jul 2008) | 1 line Fix misspeeld method name (negative) ........ r65176 | amaury.forgeotdarc | 2008-07-21 23:36:24 +0200 (Mon, 21 Jul 2008) | 4 lines Increment version number in NEWS file, and move items that were added after 2.6b2. (I thought there was a script to automate this kind of updates) ........ r65177 | amaury.forgeotdarc | 2008-07-22 00:00:38 +0200 (Tue, 22 Jul 2008) | 5 lines Issue2378: pdb would delete free variables when stepping into a class statement. The problem was introduced by r53954, the correction is to restore the symmetry between PyFrame_FastToLocals and PyFrame_LocalsToFast ........ r65178 | benjamin.peterson | 2008-07-22 00:05:34 +0200 (Tue, 22 Jul 2008) | 1 line don't use assert statement ........ r65183 | ronald.oussoren | 2008-07-22 09:06:00 +0200 (Tue, 22 Jul 2008) | 2 lines Fix buglet in fix for issue3381 ........ r65184 | ronald.oussoren | 2008-07-22 09:06:33 +0200 (Tue, 22 Jul 2008) | 2 lines Fix build issue on OSX 10.4, somehow this wasn't committed before. ........ r65187 | raymond.hettinger | 2008-07-22 20:54:02 +0200 (Tue, 22 Jul 2008) | 1 line Remove out-of-date section on Exact/Inexact. ........ r65188 | raymond.hettinger | 2008-07-22 21:00:47 +0200 (Tue, 22 Jul 2008) | 1 line Tuples now have both count() and index(). ........ r65189 | raymond.hettinger | 2008-07-22 21:03:05 +0200 (Tue, 22 Jul 2008) | 1 line Fix credits for math.sum() ........ r65190 | raymond.hettinger | 2008-07-22 21:18:50 +0200 (Tue, 22 Jul 2008) | 1 line One more attribution. ........ r65192 | benjamin.peterson | 2008-07-23 01:44:37 +0200 (Wed, 23 Jul 2008) | 1 line remove unneeded import ........ r65194 | benjamin.peterson | 2008-07-23 15:25:06 +0200 (Wed, 23 Jul 2008) | 1 line use isinstance ........
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only when the function is called. [#]_
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Merged revisions 62350-62355,62358-62359,62364-62365,62370,62372-62375,62378-62379,62381 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r62350 | nick.coghlan | 2008-04-15 12:25:31 +0200 (Tue, 15 Apr 2008) | 1 line Issue 2439: add pkgutils.get_data() as a convenience wrapper for the PEP 302 get_data() API (contributed by Paul Moore) ........ r62351 | nick.coghlan | 2008-04-15 12:28:14 +0200 (Tue, 15 Apr 2008) | 1 line Add test file missing from rev 62350 ........ r62352 | benjamin.peterson | 2008-04-15 13:58:46 +0200 (Tue, 15 Apr 2008) | 2 lines Add myself to Doc/ACKS.txt ........ r62353 | andrew.kuchling | 2008-04-15 15:10:07 +0200 (Tue, 15 Apr 2008) | 6 lines Add *,**,@ to index, as suggested by http://farmdev.com/thoughts/24/what-does-the-def-star-variable-or-def-asterisk-parameter-syntax-do-in-python-/ The right entry type to use isn't clear; operator seems wrong, because *,**,@ aren't being used in expressions here. I put them as 'statement'; 'syntax' might be better. ........ r62354 | andrew.kuchling | 2008-04-15 15:10:41 +0200 (Tue, 15 Apr 2008) | 1 line Typo fix ........ r62355 | mark.dickinson | 2008-04-15 22:51:18 +0200 (Tue, 15 Apr 2008) | 3 lines Fix for possible signed overflow: the behaviour of -LONG_MIN is undefined in ANSI C. ........ r62358 | jeroen.ruigrok | 2008-04-16 14:47:01 +0200 (Wed, 16 Apr 2008) | 2 lines Reformat to 80 columns prior to adding documentation. ........ r62359 | jeroen.ruigrok | 2008-04-16 14:57:43 +0200 (Wed, 16 Apr 2008) | 2 lines Add details about the return value for mmap.flush(). ........ r62364 | raymond.hettinger | 2008-04-17 12:48:31 +0200 (Thu, 17 Apr 2008) | 1 line Issue 2648: Add leading zero to money format recipe in the docs. ........ r62365 | jeroen.ruigrok | 2008-04-17 14:39:45 +0200 (Thu, 17 Apr 2008) | 2 lines Be consistent in the use of read-only. ........ r62370 | andrew.kuchling | 2008-04-17 22:44:06 +0200 (Thu, 17 Apr 2008) | 1 line Typo fixes ........ r62372 | andrew.kuchling | 2008-04-18 04:40:47 +0200 (Fri, 18 Apr 2008) | 1 line Use correct parameter name ........ r62373 | andrew.kuchling | 2008-04-18 18:53:09 +0200 (Fri, 18 Apr 2008) | 1 line #2654: fix typo ........ r62374 | andrew.kuchling | 2008-04-18 20:28:23 +0200 (Fri, 18 Apr 2008) | 4 lines Remove personal note from Jim Roskind; it no longer applies, and the e-mail address is for a previous employer. Can we move the big long copyright statement into a sidebar or something? ........ r62375 | andrew.kuchling | 2008-04-18 20:39:55 +0200 (Fri, 18 Apr 2008) | 1 line Rewrite introductory section, and remove old section. (It was already commented-out, but why keep it?) ........ r62378 | skip.montanaro | 2008-04-18 22:35:46 +0200 (Fri, 18 Apr 2008) | 1 line resolve issue 2014 ........ r62379 | benjamin.peterson | 2008-04-18 22:45:33 +0200 (Fri, 18 Apr 2008) | 2 lines Fix indentation in sysmodule.c ........ r62381 | amaury.forgeotdarc | 2008-04-19 01:31:33 +0200 (Sat, 19 Apr 2008) | 3 lines Some tests did not pass on repeated calls (regrtest -R::) Perform additional cleanup, mostly deleting from sys.modules, or clearing the warnings registry. ........
2008-04-18 21:55:37 -03:00
.. index::
single: @ (at); function definition
Merged revisions 62350-62355,62358-62359,62364-62365,62370,62372-62375,62378-62379,62381 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r62350 | nick.coghlan | 2008-04-15 12:25:31 +0200 (Tue, 15 Apr 2008) | 1 line Issue 2439: add pkgutils.get_data() as a convenience wrapper for the PEP 302 get_data() API (contributed by Paul Moore) ........ r62351 | nick.coghlan | 2008-04-15 12:28:14 +0200 (Tue, 15 Apr 2008) | 1 line Add test file missing from rev 62350 ........ r62352 | benjamin.peterson | 2008-04-15 13:58:46 +0200 (Tue, 15 Apr 2008) | 2 lines Add myself to Doc/ACKS.txt ........ r62353 | andrew.kuchling | 2008-04-15 15:10:07 +0200 (Tue, 15 Apr 2008) | 6 lines Add *,**,@ to index, as suggested by http://farmdev.com/thoughts/24/what-does-the-def-star-variable-or-def-asterisk-parameter-syntax-do-in-python-/ The right entry type to use isn't clear; operator seems wrong, because *,**,@ aren't being used in expressions here. I put them as 'statement'; 'syntax' might be better. ........ r62354 | andrew.kuchling | 2008-04-15 15:10:41 +0200 (Tue, 15 Apr 2008) | 1 line Typo fix ........ r62355 | mark.dickinson | 2008-04-15 22:51:18 +0200 (Tue, 15 Apr 2008) | 3 lines Fix for possible signed overflow: the behaviour of -LONG_MIN is undefined in ANSI C. ........ r62358 | jeroen.ruigrok | 2008-04-16 14:47:01 +0200 (Wed, 16 Apr 2008) | 2 lines Reformat to 80 columns prior to adding documentation. ........ r62359 | jeroen.ruigrok | 2008-04-16 14:57:43 +0200 (Wed, 16 Apr 2008) | 2 lines Add details about the return value for mmap.flush(). ........ r62364 | raymond.hettinger | 2008-04-17 12:48:31 +0200 (Thu, 17 Apr 2008) | 1 line Issue 2648: Add leading zero to money format recipe in the docs. ........ r62365 | jeroen.ruigrok | 2008-04-17 14:39:45 +0200 (Thu, 17 Apr 2008) | 2 lines Be consistent in the use of read-only. ........ r62370 | andrew.kuchling | 2008-04-17 22:44:06 +0200 (Thu, 17 Apr 2008) | 1 line Typo fixes ........ r62372 | andrew.kuchling | 2008-04-18 04:40:47 +0200 (Fri, 18 Apr 2008) | 1 line Use correct parameter name ........ r62373 | andrew.kuchling | 2008-04-18 18:53:09 +0200 (Fri, 18 Apr 2008) | 1 line #2654: fix typo ........ r62374 | andrew.kuchling | 2008-04-18 20:28:23 +0200 (Fri, 18 Apr 2008) | 4 lines Remove personal note from Jim Roskind; it no longer applies, and the e-mail address is for a previous employer. Can we move the big long copyright statement into a sidebar or something? ........ r62375 | andrew.kuchling | 2008-04-18 20:39:55 +0200 (Fri, 18 Apr 2008) | 1 line Rewrite introductory section, and remove old section. (It was already commented-out, but why keep it?) ........ r62378 | skip.montanaro | 2008-04-18 22:35:46 +0200 (Fri, 18 Apr 2008) | 1 line resolve issue 2014 ........ r62379 | benjamin.peterson | 2008-04-18 22:45:33 +0200 (Fri, 18 Apr 2008) | 2 lines Fix indentation in sysmodule.c ........ r62381 | amaury.forgeotdarc | 2008-04-19 01:31:33 +0200 (Sat, 19 Apr 2008) | 3 lines Some tests did not pass on repeated calls (regrtest -R::) Perform additional cleanup, mostly deleting from sys.modules, or clearing the warnings registry. ........
2008-04-18 21:55:37 -03:00
Merged revisions 59259-59274 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r59260 | lars.gustaebel | 2007-12-01 22:02:12 +0100 (Sat, 01 Dec 2007) | 5 lines Issue #1531: Read fileobj from the current offset, do not seek to the start. (will backport to 2.5) ........ r59262 | georg.brandl | 2007-12-01 23:24:47 +0100 (Sat, 01 Dec 2007) | 4 lines Document PyEval_* functions from ceval.c. Credits to Michael Sloan from GHOP. ........ r59263 | georg.brandl | 2007-12-01 23:27:56 +0100 (Sat, 01 Dec 2007) | 2 lines Add a few refcount data entries. ........ r59264 | georg.brandl | 2007-12-01 23:38:48 +0100 (Sat, 01 Dec 2007) | 4 lines Add test suite for cmd module. Written by Michael Schneider for GHOP. ........ r59265 | georg.brandl | 2007-12-01 23:42:46 +0100 (Sat, 01 Dec 2007) | 3 lines Add examples to the ElementTree documentation. Written by h4wk.cz for GHOP. ........ r59266 | georg.brandl | 2007-12-02 00:12:45 +0100 (Sun, 02 Dec 2007) | 3 lines Add "Using Python on Windows" document, by Robert Lehmann. Written for GHOP. ........ r59271 | georg.brandl | 2007-12-02 15:34:34 +0100 (Sun, 02 Dec 2007) | 3 lines Add example to mmap docs. Written for GHOP by Rafal Rawicki. ........ r59272 | georg.brandl | 2007-12-02 15:37:29 +0100 (Sun, 02 Dec 2007) | 2 lines Convert bdb.rst line endings to Unix style. ........ r59274 | georg.brandl | 2007-12-02 15:58:50 +0100 (Sun, 02 Dec 2007) | 4 lines Add more entries to the glossary. Written by Jeff Wheeler for GHOP. ........
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A function definition may be wrapped by one or more :term:`decorator` expressions.
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Decorator expressions are evaluated when the function is defined, in the scope
that contains the function definition. The result must be a callable, which is
invoked with the function object as the only argument. The returned value is
bound to the function name instead of the function object. Multiple decorators
are applied in nested fashion. For example, the following code ::
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@f1(arg)
@f2
def func(): pass
is roughly equivalent to ::
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def func(): pass
func = f1(arg)(f2(func))
except that the original function is not temporarily bound to the name ``func``.
.. versionchanged:: 3.9
Functions may be decorated with any valid
:token:`~python-grammar:assignment_expression`. Previously, the grammar was
much more restrictive; see :pep:`614` for details.
.. index::
triple: default; parameter; value
single: argument; function definition
single: = (equals); function definition
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When one or more :term:`parameters <parameter>` have the form *parameter* ``=``
*expression*, the function is said to have "default parameter values." For a
parameter with a default value, the corresponding :term:`argument` may be
omitted from a call, in which
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case the parameter's default value is substituted. If a parameter has a default
value, all following parameters up until the "``*``" must also have a default
value --- this is a syntactic restriction that is not expressed by the grammar.
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**Default parameter values are evaluated from left to right when the function
definition is executed.** This means that the expression is evaluated once, when
the function is defined, and that the same "pre-computed" value is used for each
call. This is especially important to understand when a default parameter value is a
mutable object, such as a list or a dictionary: if the function modifies the
object (e.g. by appending an item to a list), the default parameter value is in effect
modified. This is generally not what was intended. A way around this is to use
``None`` as the default, and explicitly test for it in the body of the function,
e.g.::
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def whats_on_the_telly(penguin=None):
if penguin is None:
penguin = []
penguin.append("property of the zoo")
return penguin
Merged revisions 62350-62355,62358-62359,62364-62365,62370,62372-62375,62378-62379,62381 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r62350 | nick.coghlan | 2008-04-15 12:25:31 +0200 (Tue, 15 Apr 2008) | 1 line Issue 2439: add pkgutils.get_data() as a convenience wrapper for the PEP 302 get_data() API (contributed by Paul Moore) ........ r62351 | nick.coghlan | 2008-04-15 12:28:14 +0200 (Tue, 15 Apr 2008) | 1 line Add test file missing from rev 62350 ........ r62352 | benjamin.peterson | 2008-04-15 13:58:46 +0200 (Tue, 15 Apr 2008) | 2 lines Add myself to Doc/ACKS.txt ........ r62353 | andrew.kuchling | 2008-04-15 15:10:07 +0200 (Tue, 15 Apr 2008) | 6 lines Add *,**,@ to index, as suggested by http://farmdev.com/thoughts/24/what-does-the-def-star-variable-or-def-asterisk-parameter-syntax-do-in-python-/ The right entry type to use isn't clear; operator seems wrong, because *,**,@ aren't being used in expressions here. I put them as 'statement'; 'syntax' might be better. ........ r62354 | andrew.kuchling | 2008-04-15 15:10:41 +0200 (Tue, 15 Apr 2008) | 1 line Typo fix ........ r62355 | mark.dickinson | 2008-04-15 22:51:18 +0200 (Tue, 15 Apr 2008) | 3 lines Fix for possible signed overflow: the behaviour of -LONG_MIN is undefined in ANSI C. ........ r62358 | jeroen.ruigrok | 2008-04-16 14:47:01 +0200 (Wed, 16 Apr 2008) | 2 lines Reformat to 80 columns prior to adding documentation. ........ r62359 | jeroen.ruigrok | 2008-04-16 14:57:43 +0200 (Wed, 16 Apr 2008) | 2 lines Add details about the return value for mmap.flush(). ........ r62364 | raymond.hettinger | 2008-04-17 12:48:31 +0200 (Thu, 17 Apr 2008) | 1 line Issue 2648: Add leading zero to money format recipe in the docs. ........ r62365 | jeroen.ruigrok | 2008-04-17 14:39:45 +0200 (Thu, 17 Apr 2008) | 2 lines Be consistent in the use of read-only. ........ r62370 | andrew.kuchling | 2008-04-17 22:44:06 +0200 (Thu, 17 Apr 2008) | 1 line Typo fixes ........ r62372 | andrew.kuchling | 2008-04-18 04:40:47 +0200 (Fri, 18 Apr 2008) | 1 line Use correct parameter name ........ r62373 | andrew.kuchling | 2008-04-18 18:53:09 +0200 (Fri, 18 Apr 2008) | 1 line #2654: fix typo ........ r62374 | andrew.kuchling | 2008-04-18 20:28:23 +0200 (Fri, 18 Apr 2008) | 4 lines Remove personal note from Jim Roskind; it no longer applies, and the e-mail address is for a previous employer. Can we move the big long copyright statement into a sidebar or something? ........ r62375 | andrew.kuchling | 2008-04-18 20:39:55 +0200 (Fri, 18 Apr 2008) | 1 line Rewrite introductory section, and remove old section. (It was already commented-out, but why keep it?) ........ r62378 | skip.montanaro | 2008-04-18 22:35:46 +0200 (Fri, 18 Apr 2008) | 1 line resolve issue 2014 ........ r62379 | benjamin.peterson | 2008-04-18 22:45:33 +0200 (Fri, 18 Apr 2008) | 2 lines Fix indentation in sysmodule.c ........ r62381 | amaury.forgeotdarc | 2008-04-19 01:31:33 +0200 (Sat, 19 Apr 2008) | 3 lines Some tests did not pass on repeated calls (regrtest -R::) Perform additional cleanup, mostly deleting from sys.modules, or clearing the warnings registry. ........
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.. index::
single: / (slash); function definition
single: * (asterisk); function definition
single: **; function definition
Merged revisions 62350-62355,62358-62359,62364-62365,62370,62372-62375,62378-62379,62381 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r62350 | nick.coghlan | 2008-04-15 12:25:31 +0200 (Tue, 15 Apr 2008) | 1 line Issue 2439: add pkgutils.get_data() as a convenience wrapper for the PEP 302 get_data() API (contributed by Paul Moore) ........ r62351 | nick.coghlan | 2008-04-15 12:28:14 +0200 (Tue, 15 Apr 2008) | 1 line Add test file missing from rev 62350 ........ r62352 | benjamin.peterson | 2008-04-15 13:58:46 +0200 (Tue, 15 Apr 2008) | 2 lines Add myself to Doc/ACKS.txt ........ r62353 | andrew.kuchling | 2008-04-15 15:10:07 +0200 (Tue, 15 Apr 2008) | 6 lines Add *,**,@ to index, as suggested by http://farmdev.com/thoughts/24/what-does-the-def-star-variable-or-def-asterisk-parameter-syntax-do-in-python-/ The right entry type to use isn't clear; operator seems wrong, because *,**,@ aren't being used in expressions here. I put them as 'statement'; 'syntax' might be better. ........ r62354 | andrew.kuchling | 2008-04-15 15:10:41 +0200 (Tue, 15 Apr 2008) | 1 line Typo fix ........ r62355 | mark.dickinson | 2008-04-15 22:51:18 +0200 (Tue, 15 Apr 2008) | 3 lines Fix for possible signed overflow: the behaviour of -LONG_MIN is undefined in ANSI C. ........ r62358 | jeroen.ruigrok | 2008-04-16 14:47:01 +0200 (Wed, 16 Apr 2008) | 2 lines Reformat to 80 columns prior to adding documentation. ........ r62359 | jeroen.ruigrok | 2008-04-16 14:57:43 +0200 (Wed, 16 Apr 2008) | 2 lines Add details about the return value for mmap.flush(). ........ r62364 | raymond.hettinger | 2008-04-17 12:48:31 +0200 (Thu, 17 Apr 2008) | 1 line Issue 2648: Add leading zero to money format recipe in the docs. ........ r62365 | jeroen.ruigrok | 2008-04-17 14:39:45 +0200 (Thu, 17 Apr 2008) | 2 lines Be consistent in the use of read-only. ........ r62370 | andrew.kuchling | 2008-04-17 22:44:06 +0200 (Thu, 17 Apr 2008) | 1 line Typo fixes ........ r62372 | andrew.kuchling | 2008-04-18 04:40:47 +0200 (Fri, 18 Apr 2008) | 1 line Use correct parameter name ........ r62373 | andrew.kuchling | 2008-04-18 18:53:09 +0200 (Fri, 18 Apr 2008) | 1 line #2654: fix typo ........ r62374 | andrew.kuchling | 2008-04-18 20:28:23 +0200 (Fri, 18 Apr 2008) | 4 lines Remove personal note from Jim Roskind; it no longer applies, and the e-mail address is for a previous employer. Can we move the big long copyright statement into a sidebar or something? ........ r62375 | andrew.kuchling | 2008-04-18 20:39:55 +0200 (Fri, 18 Apr 2008) | 1 line Rewrite introductory section, and remove old section. (It was already commented-out, but why keep it?) ........ r62378 | skip.montanaro | 2008-04-18 22:35:46 +0200 (Fri, 18 Apr 2008) | 1 line resolve issue 2014 ........ r62379 | benjamin.peterson | 2008-04-18 22:45:33 +0200 (Fri, 18 Apr 2008) | 2 lines Fix indentation in sysmodule.c ........ r62381 | amaury.forgeotdarc | 2008-04-19 01:31:33 +0200 (Sat, 19 Apr 2008) | 3 lines Some tests did not pass on repeated calls (regrtest -R::) Perform additional cleanup, mostly deleting from sys.modules, or clearing the warnings registry. ........
2008-04-18 21:55:37 -03:00
Function call semantics are described in more detail in section :ref:`calls`. A
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function call always assigns values to all parameters mentioned in the parameter
list, either from positional arguments, from keyword arguments, or from default
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values. If the form "``*identifier``" is present, it is initialized to a tuple
receiving any excess positional parameters, defaulting to the empty tuple.
If the form "``**identifier``" is present, it is initialized to a new
ordered mapping receiving any excess keyword arguments, defaulting to a
new empty mapping of the same type. Parameters after "``*``" or
"``*identifier``" are keyword-only parameters and may only be passed
by keyword arguments. Parameters before "``/``" are positional-only parameters
and may only be passed by positional arguments.
.. versionchanged:: 3.8
The ``/`` function parameter syntax may be used to indicate positional-only
parameters. See :pep:`570` for details.
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.. index::
pair: function; annotations
single: ->; function annotations
single: : (colon); function annotations
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Parameters may have an :term:`annotation <function annotation>` of the form "``: expression``"
following the parameter name. Any parameter may have an annotation, even those of the form
``*identifier`` or ``**identifier``. Functions may have "return" annotation of
the form "``-> expression``" after the parameter list. These annotations can be
any valid Python expression. The presence of annotations does not change the
semantics of a function. The annotation values are available as values of
a dictionary keyed by the parameters' names in the :attr:`__annotations__`
attribute of the function object. If the ``annotations`` import from
:mod:`__future__` is used, annotations are preserved as strings at runtime which
enables postponed evaluation. Otherwise, they are evaluated when the function
definition is executed. In this case annotations may be evaluated in
a different order than they appear in the source code.
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.. index:: pair: lambda; expression
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It is also possible to create anonymous functions (functions not bound to a
name), for immediate use in expressions. This uses lambda expressions, described in
section :ref:`lambda`. Note that the lambda expression is merely a shorthand for a
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simplified function definition; a function defined in a ":keyword:`def`"
statement can be passed around or assigned to another name just like a function
defined by a lambda expression. The ":keyword:`!def`" form is actually more powerful
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since it allows the execution of multiple statements and annotations.
**Programmer's note:** Functions are first-class objects. A "``def``" statement
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executed inside a function definition defines a local function that can be
returned or passed around. Free variables used in the nested function can
access the local variables of the function containing the def. See section
:ref:`naming` for details.
.. seealso::
:pep:`3107` - Function Annotations
The original specification for function annotations.
:pep:`484` - Type Hints
Definition of a standard meaning for annotations: type hints.
:pep:`526` - Syntax for Variable Annotations
Ability to type hint variable declarations, including class
variables and instance variables
:pep:`563` - Postponed Evaluation of Annotations
Support for forward references within annotations by preserving
annotations in a string form at runtime instead of eager evaluation.
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.. _class:
Class definitions
=================
.. index::
object: class
Merged revisions 59703-59773 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r59704 | christian.heimes | 2008-01-04 04:15:05 +0100 (Fri, 04 Jan 2008) | 1 line Moved include "Python.h" in front of other imports to silence a warning. ........ r59706 | raymond.hettinger | 2008-01-04 04:22:53 +0100 (Fri, 04 Jan 2008) | 10 lines Minor fix-ups to named tuples: * Make the _replace() method respect subclassing. * Using property() to make _fields read-only wasn't a good idea. It caused len(Point._fields) to fail. * Add note to _cast() about length checking and alternative with the star-operator. ........ r59707 | jeffrey.yasskin | 2008-01-04 09:01:23 +0100 (Fri, 04 Jan 2008) | 3 lines Make math.{floor,ceil}({int,long}) return float again for backwards compatibility after r59671 made them return integral types. ........ r59709 | christian.heimes | 2008-01-04 14:21:07 +0100 (Fri, 04 Jan 2008) | 1 line Bug #1713: posixpath.ismount() claims symlink to a mountpoint is a mountpoint. ........ r59712 | lars.gustaebel | 2008-01-04 15:00:33 +0100 (Fri, 04 Jan 2008) | 5 lines Issue #1735: TarFile.extractall() now correctly sets directory permissions and times. (will backport to 2.5) ........ r59714 | andrew.kuchling | 2008-01-04 15:47:17 +0100 (Fri, 04 Jan 2008) | 1 line Update links to bug/patch tracker ........ r59716 | christian.heimes | 2008-01-04 16:23:30 +0100 (Fri, 04 Jan 2008) | 1 line Added interface to Windows' WSAIoctl and a simple example for a network sniffer. ........ r59717 | christian.heimes | 2008-01-04 16:29:00 +0100 (Fri, 04 Jan 2008) | 1 line And here is the rest of Hirokazu Yamamoto's patch for VS6.0 support. Thanks Hiro! ........ r59719 | christian.heimes | 2008-01-04 16:34:06 +0100 (Fri, 04 Jan 2008) | 1 line Reverted last transaction. It's the wrong branch. ........ r59721 | christian.heimes | 2008-01-04 16:48:06 +0100 (Fri, 04 Jan 2008) | 1 line socket.ioctl is only available on Windows ........ r59722 | andrew.kuchling | 2008-01-04 19:24:41 +0100 (Fri, 04 Jan 2008) | 1 line Fix markup ........ r59723 | andrew.kuchling | 2008-01-04 19:25:05 +0100 (Fri, 04 Jan 2008) | 1 line Fix markup ........ r59725 | guido.van.rossum | 2008-01-05 01:59:59 +0100 (Sat, 05 Jan 2008) | 3 lines Patch #1725 by Mark Dickinson, fixes incorrect conversion of -1e1000 and adds errors for -0x. ........ r59726 | guido.van.rossum | 2008-01-05 02:21:57 +0100 (Sat, 05 Jan 2008) | 2 lines Patch #1698 by Senthil: allow '@' in username when parsed by urlparse.py. ........ r59727 | raymond.hettinger | 2008-01-05 02:35:43 +0100 (Sat, 05 Jan 2008) | 1 line Improve namedtuple's _cast() method with a docstring, new name, and error-checking. ........ r59728 | raymond.hettinger | 2008-01-05 03:17:24 +0100 (Sat, 05 Jan 2008) | 1 line Add error-checking to namedtuple's _replace() method. ........ r59730 | fred.drake | 2008-01-05 05:38:38 +0100 (Sat, 05 Jan 2008) | 2 lines clean up a comment ........ r59731 | jeffrey.yasskin | 2008-01-05 09:47:13 +0100 (Sat, 05 Jan 2008) | 11 lines Continue rolling back pep-3141 changes that changed behavior from 2.5. This round included: * Revert round to its 2.6 behavior (half away from 0). * Because round, floor, and ceil always return float again, it's no longer necessary to have them delegate to __xxx___, so I've ripped that out of their implementations and the Real ABC. This also helps in implementing types that work in both 2.6 and 3.0: you return int from the __xxx__ methods, and let it get enabled by the version upgrade. * Make pow(-1, .5) raise a ValueError again. ........ r59736 | andrew.kuchling | 2008-01-05 16:13:49 +0100 (Sat, 05 Jan 2008) | 1 line Fix comment typo ........ r59738 | thomas.heller | 2008-01-05 18:15:44 +0100 (Sat, 05 Jan 2008) | 1 line Add myself. ........ r59739 | georg.brandl | 2008-01-05 18:49:17 +0100 (Sat, 05 Jan 2008) | 2 lines Fix C++-style comment. ........ r59742 | georg.brandl | 2008-01-05 20:28:16 +0100 (Sat, 05 Jan 2008) | 2 lines Remove with_statement future imports from 2.6 docs. ........ r59743 | georg.brandl | 2008-01-05 20:29:45 +0100 (Sat, 05 Jan 2008) | 2 lines Simplify index entries; fix #1712. ........ r59744 | georg.brandl | 2008-01-05 20:44:22 +0100 (Sat, 05 Jan 2008) | 2 lines Doc patch #1730 from Robin Stocker; minor corrections mostly to os.rst. ........ r59749 | georg.brandl | 2008-01-05 21:29:13 +0100 (Sat, 05 Jan 2008) | 2 lines Revert socket.rst to unix-eol. ........ r59750 | georg.brandl | 2008-01-05 21:33:46 +0100 (Sat, 05 Jan 2008) | 2 lines Set native svn:eol-style property for text files. ........ r59752 | georg.brandl | 2008-01-05 21:46:29 +0100 (Sat, 05 Jan 2008) | 2 lines #1719: capitalization error in "UuidCreate". ........ r59753 | georg.brandl | 2008-01-05 22:02:25 +0100 (Sat, 05 Jan 2008) | 2 lines Repair markup. ........ r59754 | georg.brandl | 2008-01-05 22:10:50 +0100 (Sat, 05 Jan 2008) | 2 lines Use markup. ........ r59757 | christian.heimes | 2008-01-05 22:35:52 +0100 (Sat, 05 Jan 2008) | 1 line Final adjustments for #1601 ........ r59758 | guido.van.rossum | 2008-01-05 23:19:06 +0100 (Sat, 05 Jan 2008) | 3 lines Patch #1637: fix urlparse for URLs like 'http://x.com?arg=/foo'. Fix by John Nagle. ........ r59759 | guido.van.rossum | 2008-01-05 23:20:01 +0100 (Sat, 05 Jan 2008) | 2 lines Add John Nagle (of issue #1637). ........ r59765 | raymond.hettinger | 2008-01-06 10:02:24 +0100 (Sun, 06 Jan 2008) | 1 line Small code simplification. Forgot that classmethods can be called from intances. ........ r59766 | martin.v.loewis | 2008-01-06 11:09:48 +0100 (Sun, 06 Jan 2008) | 2 lines Use vcbuild for VS 2009. ........ r59767 | martin.v.loewis | 2008-01-06 12:03:43 +0100 (Sun, 06 Jan 2008) | 2 lines Package using VS 2008. ........ r59768 | martin.v.loewis | 2008-01-06 12:13:16 +0100 (Sun, 06 Jan 2008) | 2 lines Don't try to package msvcr90 for the moment. ........ r59769 | georg.brandl | 2008-01-06 15:17:36 +0100 (Sun, 06 Jan 2008) | 4 lines #1696393: don't check for '.' and '..' in ntpath.walk since they aren't returned from os.listdir anymore. Reported by Michael Haggerty. ........ r59770 | georg.brandl | 2008-01-06 15:27:15 +0100 (Sun, 06 Jan 2008) | 3 lines #1742: don't raise exception on os.path.relpath("a", "a"), but return os.curdir. Reported by Jesse Towner. ........ r59771 | georg.brandl | 2008-01-06 15:33:52 +0100 (Sun, 06 Jan 2008) | 2 lines #1591: Clarify docstring of Popen3. ........ r59772 | georg.brandl | 2008-01-06 16:30:34 +0100 (Sun, 06 Jan 2008) | 2 lines #1680: fix context manager example function name. ........ r59773 | georg.brandl | 2008-01-06 16:34:57 +0100 (Sun, 06 Jan 2008) | 2 lines #1755097: document default values for [].sort() and sorted(). ........
2008-01-06 12:59:19 -04:00
statement: class
pair: class; definition
pair: class; name
pair: name; binding
pair: execution; frame
Merged revisions 59703-59773 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r59704 | christian.heimes | 2008-01-04 04:15:05 +0100 (Fri, 04 Jan 2008) | 1 line Moved include "Python.h" in front of other imports to silence a warning. ........ r59706 | raymond.hettinger | 2008-01-04 04:22:53 +0100 (Fri, 04 Jan 2008) | 10 lines Minor fix-ups to named tuples: * Make the _replace() method respect subclassing. * Using property() to make _fields read-only wasn't a good idea. It caused len(Point._fields) to fail. * Add note to _cast() about length checking and alternative with the star-operator. ........ r59707 | jeffrey.yasskin | 2008-01-04 09:01:23 +0100 (Fri, 04 Jan 2008) | 3 lines Make math.{floor,ceil}({int,long}) return float again for backwards compatibility after r59671 made them return integral types. ........ r59709 | christian.heimes | 2008-01-04 14:21:07 +0100 (Fri, 04 Jan 2008) | 1 line Bug #1713: posixpath.ismount() claims symlink to a mountpoint is a mountpoint. ........ r59712 | lars.gustaebel | 2008-01-04 15:00:33 +0100 (Fri, 04 Jan 2008) | 5 lines Issue #1735: TarFile.extractall() now correctly sets directory permissions and times. (will backport to 2.5) ........ r59714 | andrew.kuchling | 2008-01-04 15:47:17 +0100 (Fri, 04 Jan 2008) | 1 line Update links to bug/patch tracker ........ r59716 | christian.heimes | 2008-01-04 16:23:30 +0100 (Fri, 04 Jan 2008) | 1 line Added interface to Windows' WSAIoctl and a simple example for a network sniffer. ........ r59717 | christian.heimes | 2008-01-04 16:29:00 +0100 (Fri, 04 Jan 2008) | 1 line And here is the rest of Hirokazu Yamamoto's patch for VS6.0 support. Thanks Hiro! ........ r59719 | christian.heimes | 2008-01-04 16:34:06 +0100 (Fri, 04 Jan 2008) | 1 line Reverted last transaction. It's the wrong branch. ........ r59721 | christian.heimes | 2008-01-04 16:48:06 +0100 (Fri, 04 Jan 2008) | 1 line socket.ioctl is only available on Windows ........ r59722 | andrew.kuchling | 2008-01-04 19:24:41 +0100 (Fri, 04 Jan 2008) | 1 line Fix markup ........ r59723 | andrew.kuchling | 2008-01-04 19:25:05 +0100 (Fri, 04 Jan 2008) | 1 line Fix markup ........ r59725 | guido.van.rossum | 2008-01-05 01:59:59 +0100 (Sat, 05 Jan 2008) | 3 lines Patch #1725 by Mark Dickinson, fixes incorrect conversion of -1e1000 and adds errors for -0x. ........ r59726 | guido.van.rossum | 2008-01-05 02:21:57 +0100 (Sat, 05 Jan 2008) | 2 lines Patch #1698 by Senthil: allow '@' in username when parsed by urlparse.py. ........ r59727 | raymond.hettinger | 2008-01-05 02:35:43 +0100 (Sat, 05 Jan 2008) | 1 line Improve namedtuple's _cast() method with a docstring, new name, and error-checking. ........ r59728 | raymond.hettinger | 2008-01-05 03:17:24 +0100 (Sat, 05 Jan 2008) | 1 line Add error-checking to namedtuple's _replace() method. ........ r59730 | fred.drake | 2008-01-05 05:38:38 +0100 (Sat, 05 Jan 2008) | 2 lines clean up a comment ........ r59731 | jeffrey.yasskin | 2008-01-05 09:47:13 +0100 (Sat, 05 Jan 2008) | 11 lines Continue rolling back pep-3141 changes that changed behavior from 2.5. This round included: * Revert round to its 2.6 behavior (half away from 0). * Because round, floor, and ceil always return float again, it's no longer necessary to have them delegate to __xxx___, so I've ripped that out of their implementations and the Real ABC. This also helps in implementing types that work in both 2.6 and 3.0: you return int from the __xxx__ methods, and let it get enabled by the version upgrade. * Make pow(-1, .5) raise a ValueError again. ........ r59736 | andrew.kuchling | 2008-01-05 16:13:49 +0100 (Sat, 05 Jan 2008) | 1 line Fix comment typo ........ r59738 | thomas.heller | 2008-01-05 18:15:44 +0100 (Sat, 05 Jan 2008) | 1 line Add myself. ........ r59739 | georg.brandl | 2008-01-05 18:49:17 +0100 (Sat, 05 Jan 2008) | 2 lines Fix C++-style comment. ........ r59742 | georg.brandl | 2008-01-05 20:28:16 +0100 (Sat, 05 Jan 2008) | 2 lines Remove with_statement future imports from 2.6 docs. ........ r59743 | georg.brandl | 2008-01-05 20:29:45 +0100 (Sat, 05 Jan 2008) | 2 lines Simplify index entries; fix #1712. ........ r59744 | georg.brandl | 2008-01-05 20:44:22 +0100 (Sat, 05 Jan 2008) | 2 lines Doc patch #1730 from Robin Stocker; minor corrections mostly to os.rst. ........ r59749 | georg.brandl | 2008-01-05 21:29:13 +0100 (Sat, 05 Jan 2008) | 2 lines Revert socket.rst to unix-eol. ........ r59750 | georg.brandl | 2008-01-05 21:33:46 +0100 (Sat, 05 Jan 2008) | 2 lines Set native svn:eol-style property for text files. ........ r59752 | georg.brandl | 2008-01-05 21:46:29 +0100 (Sat, 05 Jan 2008) | 2 lines #1719: capitalization error in "UuidCreate". ........ r59753 | georg.brandl | 2008-01-05 22:02:25 +0100 (Sat, 05 Jan 2008) | 2 lines Repair markup. ........ r59754 | georg.brandl | 2008-01-05 22:10:50 +0100 (Sat, 05 Jan 2008) | 2 lines Use markup. ........ r59757 | christian.heimes | 2008-01-05 22:35:52 +0100 (Sat, 05 Jan 2008) | 1 line Final adjustments for #1601 ........ r59758 | guido.van.rossum | 2008-01-05 23:19:06 +0100 (Sat, 05 Jan 2008) | 3 lines Patch #1637: fix urlparse for URLs like 'http://x.com?arg=/foo'. Fix by John Nagle. ........ r59759 | guido.van.rossum | 2008-01-05 23:20:01 +0100 (Sat, 05 Jan 2008) | 2 lines Add John Nagle (of issue #1637). ........ r59765 | raymond.hettinger | 2008-01-06 10:02:24 +0100 (Sun, 06 Jan 2008) | 1 line Small code simplification. Forgot that classmethods can be called from intances. ........ r59766 | martin.v.loewis | 2008-01-06 11:09:48 +0100 (Sun, 06 Jan 2008) | 2 lines Use vcbuild for VS 2009. ........ r59767 | martin.v.loewis | 2008-01-06 12:03:43 +0100 (Sun, 06 Jan 2008) | 2 lines Package using VS 2008. ........ r59768 | martin.v.loewis | 2008-01-06 12:13:16 +0100 (Sun, 06 Jan 2008) | 2 lines Don't try to package msvcr90 for the moment. ........ r59769 | georg.brandl | 2008-01-06 15:17:36 +0100 (Sun, 06 Jan 2008) | 4 lines #1696393: don't check for '.' and '..' in ntpath.walk since they aren't returned from os.listdir anymore. Reported by Michael Haggerty. ........ r59770 | georg.brandl | 2008-01-06 15:27:15 +0100 (Sun, 06 Jan 2008) | 3 lines #1742: don't raise exception on os.path.relpath("a", "a"), but return os.curdir. Reported by Jesse Towner. ........ r59771 | georg.brandl | 2008-01-06 15:33:52 +0100 (Sun, 06 Jan 2008) | 2 lines #1591: Clarify docstring of Popen3. ........ r59772 | georg.brandl | 2008-01-06 16:30:34 +0100 (Sun, 06 Jan 2008) | 2 lines #1680: fix context manager example function name. ........ r59773 | georg.brandl | 2008-01-06 16:34:57 +0100 (Sun, 06 Jan 2008) | 2 lines #1755097: document default values for [].sort() and sorted(). ........
2008-01-06 12:59:19 -04:00
single: inheritance
Merged revisions 65012,65035,65037-65040,65048,65057,65077,65091-65095,65097-65099,65127-65128,65131,65133-65136,65139,65149-65151,65155,65158-65159,65176-65178,65183-65184,65187-65190,65192,65194 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r65012 | jesse.noller | 2008-07-16 15:24:06 +0200 (Wed, 16 Jul 2008) | 2 lines Apply patch for issue 3090: ARCHFLAGS parsing incorrect ........ r65035 | georg.brandl | 2008-07-16 23:19:28 +0200 (Wed, 16 Jul 2008) | 2 lines #3045: fix pydoc behavior for TEMP path with spaces. ........ r65037 | georg.brandl | 2008-07-16 23:31:41 +0200 (Wed, 16 Jul 2008) | 2 lines #1608818: errno can get set by every call to readdir(). ........ r65038 | georg.brandl | 2008-07-17 00:04:20 +0200 (Thu, 17 Jul 2008) | 2 lines #3305: self->stream can be NULL. ........ r65039 | georg.brandl | 2008-07-17 00:09:17 +0200 (Thu, 17 Jul 2008) | 2 lines #3345: fix docstring. ........ r65040 | georg.brandl | 2008-07-17 00:33:18 +0200 (Thu, 17 Jul 2008) | 2 lines #3312: fix two sqlite3 crashes. ........ r65048 | georg.brandl | 2008-07-17 01:35:54 +0200 (Thu, 17 Jul 2008) | 2 lines #3388: add a paragraph about using "with" for file objects. ........ r65057 | gregory.p.smith | 2008-07-17 05:13:05 +0200 (Thu, 17 Jul 2008) | 2 lines news note for r63052 ........ r65077 | jesse.noller | 2008-07-17 23:01:05 +0200 (Thu, 17 Jul 2008) | 3 lines Fix issue 3395, update _debugInfo to be _debug_info ........ r65091 | ronald.oussoren | 2008-07-18 07:48:03 +0200 (Fri, 18 Jul 2008) | 2 lines Last bit of a fix for issue3381 (addon for my patch in r65061) ........ r65092 | vinay.sajip | 2008-07-18 10:59:06 +0200 (Fri, 18 Jul 2008) | 1 line Issue #3389: Allow resolving dotted names for handlers in logging configuration files. Thanks to Philip Jenvey for the patch. ........ r65093 | vinay.sajip | 2008-07-18 11:00:00 +0200 (Fri, 18 Jul 2008) | 1 line Issue #3389: Allow resolving dotted names for handlers in logging configuration files. Thanks to Philip Jenvey for the patch. ........ r65094 | vinay.sajip | 2008-07-18 11:00:35 +0200 (Fri, 18 Jul 2008) | 1 line Issue #3389: Allow resolving dotted names for handlers in logging configuration files. Thanks to Philip Jenvey for the patch. ........ r65095 | vinay.sajip | 2008-07-18 11:01:10 +0200 (Fri, 18 Jul 2008) | 1 line Issue #3389: Allow resolving dotted names for handlers in logging configuration files. Thanks to Philip Jenvey for the patch. ........ r65097 | georg.brandl | 2008-07-18 12:20:59 +0200 (Fri, 18 Jul 2008) | 2 lines Remove duplicate entry in __all__. ........ r65098 | georg.brandl | 2008-07-18 12:29:30 +0200 (Fri, 18 Jul 2008) | 2 lines Correct attribute name. ........ r65099 | georg.brandl | 2008-07-18 13:15:06 +0200 (Fri, 18 Jul 2008) | 3 lines Document the different meaning of precision for {:f} and {:g}. Also document how inf and nan are formatted. #3404. ........ r65127 | raymond.hettinger | 2008-07-19 02:42:03 +0200 (Sat, 19 Jul 2008) | 1 line Improve accuracy of gamma test function ........ r65128 | raymond.hettinger | 2008-07-19 02:43:00 +0200 (Sat, 19 Jul 2008) | 1 line Add recipe to the itertools docs. ........ r65131 | georg.brandl | 2008-07-19 12:08:55 +0200 (Sat, 19 Jul 2008) | 2 lines #3378: in case of no memory, don't leak even more memory. :) ........ r65133 | georg.brandl | 2008-07-19 14:39:10 +0200 (Sat, 19 Jul 2008) | 3 lines #3302: fix segfaults when passing None for arguments that can't be NULL for the C functions. ........ r65134 | georg.brandl | 2008-07-19 14:46:12 +0200 (Sat, 19 Jul 2008) | 2 lines #3303: fix crash with invalid Py_DECREF in strcoll(). ........ r65135 | georg.brandl | 2008-07-19 15:00:22 +0200 (Sat, 19 Jul 2008) | 3 lines #3319: don't raise ZeroDivisionError if number of rounds is so low that benchtime is zero. ........ r65136 | georg.brandl | 2008-07-19 15:09:42 +0200 (Sat, 19 Jul 2008) | 3 lines #3323: mention that if inheriting from a class without __slots__, the subclass will have a __dict__ available too. ........ r65139 | georg.brandl | 2008-07-19 15:48:44 +0200 (Sat, 19 Jul 2008) | 2 lines Add ordering info for findall and finditer. ........ r65149 | raymond.hettinger | 2008-07-20 01:21:57 +0200 (Sun, 20 Jul 2008) | 1 line Fix compress() recipe in docs to use itertools. ........ r65150 | raymond.hettinger | 2008-07-20 01:58:47 +0200 (Sun, 20 Jul 2008) | 1 line Clean-up itertools docs and recipes. ........ r65151 | gregory.p.smith | 2008-07-20 02:22:08 +0200 (Sun, 20 Jul 2008) | 9 lines fix issue3120 - don't truncate handles on 64-bit Windows. This is still messy, realistically PC/_subprocess.c should never cast pointers to python numbers and back at all. I don't have a 64-bit windows build environment because microsoft apparently thinks that should cost money. Time to watch the buildbots. It builds and passes tests on 32-bit windows. ........ r65155 | georg.brandl | 2008-07-20 13:50:29 +0200 (Sun, 20 Jul 2008) | 2 lines #926501: add info where to put the docstring. ........ r65158 | neal.norwitz | 2008-07-20 21:35:23 +0200 (Sun, 20 Jul 2008) | 1 line Fix a couple of names in error messages that were wrong ........ r65159 | neal.norwitz | 2008-07-20 22:39:36 +0200 (Sun, 20 Jul 2008) | 1 line Fix misspeeld method name (negative) ........ r65176 | amaury.forgeotdarc | 2008-07-21 23:36:24 +0200 (Mon, 21 Jul 2008) | 4 lines Increment version number in NEWS file, and move items that were added after 2.6b2. (I thought there was a script to automate this kind of updates) ........ r65177 | amaury.forgeotdarc | 2008-07-22 00:00:38 +0200 (Tue, 22 Jul 2008) | 5 lines Issue2378: pdb would delete free variables when stepping into a class statement. The problem was introduced by r53954, the correction is to restore the symmetry between PyFrame_FastToLocals and PyFrame_LocalsToFast ........ r65178 | benjamin.peterson | 2008-07-22 00:05:34 +0200 (Tue, 22 Jul 2008) | 1 line don't use assert statement ........ r65183 | ronald.oussoren | 2008-07-22 09:06:00 +0200 (Tue, 22 Jul 2008) | 2 lines Fix buglet in fix for issue3381 ........ r65184 | ronald.oussoren | 2008-07-22 09:06:33 +0200 (Tue, 22 Jul 2008) | 2 lines Fix build issue on OSX 10.4, somehow this wasn't committed before. ........ r65187 | raymond.hettinger | 2008-07-22 20:54:02 +0200 (Tue, 22 Jul 2008) | 1 line Remove out-of-date section on Exact/Inexact. ........ r65188 | raymond.hettinger | 2008-07-22 21:00:47 +0200 (Tue, 22 Jul 2008) | 1 line Tuples now have both count() and index(). ........ r65189 | raymond.hettinger | 2008-07-22 21:03:05 +0200 (Tue, 22 Jul 2008) | 1 line Fix credits for math.sum() ........ r65190 | raymond.hettinger | 2008-07-22 21:18:50 +0200 (Tue, 22 Jul 2008) | 1 line One more attribution. ........ r65192 | benjamin.peterson | 2008-07-23 01:44:37 +0200 (Wed, 23 Jul 2008) | 1 line remove unneeded import ........ r65194 | benjamin.peterson | 2008-07-23 15:25:06 +0200 (Wed, 23 Jul 2008) | 1 line use isinstance ........
2008-07-23 13:10:53 -03:00
single: docstring
single: () (parentheses); class definition
single: , (comma); expression list
single: : (colon); compound statement
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A class definition defines a class object (see section :ref:`types`):
.. productionlist:: python-grammar
classdef: [`decorators`] "class" `classname` [`inheritance`] ":" `suite`
inheritance: "(" [`argument_list`] ")"
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classname: `identifier`
A class definition is an executable statement. The inheritance list usually
gives a list of base classes (see :ref:`metaclasses` for more advanced uses), so
each item in the list should evaluate to a class object which allows
subclassing. Classes without an inheritance list inherit, by default, from the
base class :class:`object`; hence, ::
class Foo:
pass
is equivalent to ::
class Foo(object):
pass
The class's suite is then executed in a new execution frame (see :ref:`naming`),
using a newly created local namespace and the original global namespace.
(Usually, the suite contains mostly function definitions.) When the class's
suite finishes execution, its execution frame is discarded but its local
namespace is saved. [#]_ A class object is then created using the inheritance
list for the base classes and the saved local namespace for the attribute
dictionary. The class name is bound to this class object in the original local
namespace.
The order in which attributes are defined in the class body is preserved
in the new class's ``__dict__``. Note that this is reliable only right
after the class is created and only for classes that were defined using
the definition syntax.
Class creation can be customized heavily using :ref:`metaclasses <metaclasses>`.
2007-08-15 11:28:22 -03:00
.. index::
single: @ (at); class definition
Classes can also be decorated: just like when decorating functions, ::
@f1(arg)
@f2
class Foo: pass
is roughly equivalent to ::
class Foo: pass
Foo = f1(arg)(f2(Foo))
The evaluation rules for the decorator expressions are the same as for function
decorators. The result is then bound to the class name.
.. versionchanged:: 3.9
Classes may be decorated with any valid
:token:`~python-grammar:assignment_expression`. Previously, the grammar was
much more restrictive; see :pep:`614` for details.
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**Programmer's note:** Variables defined in the class definition are class
attributes; they are shared by instances. Instance attributes can be set in a
method with ``self.name = value``. Both class and instance attributes are
accessible through the notation "``self.name``", and an instance attribute hides
a class attribute with the same name when accessed in this way. Class
attributes can be used as defaults for instance attributes, but using mutable
values there can lead to unexpected results. :ref:`Descriptors <descriptors>`
can be used to create instance variables with different implementation details.
2007-08-15 11:28:22 -03:00
.. seealso::
:pep:`3115` - Metaclasses in Python 3000
The proposal that changed the declaration of metaclasses to the current
syntax, and the semantics for how classes with metaclasses are
constructed.
:pep:`3129` - Class Decorators
The proposal that added class decorators. Function and method decorators
were introduced in :pep:`318`.
.. _async:
Coroutines
==========
Issue #24400: Introduce a distinct type for 'async def' coroutines. Summary of changes: 1. Coroutines now have a distinct, separate from generators type at the C level: PyGen_Type, and a new typedef PyCoroObject. PyCoroObject shares the initial segment of struct layout with PyGenObject, making it possible to reuse existing generators machinery. The new type is exposed as 'types.CoroutineType'. As a consequence of having a new type, CO_GENERATOR flag is no longer applied to coroutines. 2. Having a separate type for coroutines made it possible to add an __await__ method to the type. Although it is not used by the interpreter (see details on that below), it makes coroutines naturally (without using __instancecheck__) conform to collections.abc.Coroutine and collections.abc.Awaitable ABCs. [The __instancecheck__ is still used for generator-based coroutines, as we don't want to add __await__ for generators.] 3. Add new opcode: GET_YIELD_FROM_ITER. The opcode is needed to allow passing native coroutines to the YIELD_FROM opcode. Before this change, 'yield from o' expression was compiled to: (o) GET_ITER LOAD_CONST YIELD_FROM Now, we use GET_YIELD_FROM_ITER instead of GET_ITER. The reason for adding a new opcode is that GET_ITER is used in some contexts (such as 'for .. in' loops) where passing a coroutine object is invalid. 4. Add two new introspection functions to the inspec module: getcoroutinestate(c) and getcoroutinelocals(c). 5. inspect.iscoroutine(o) is updated to test if 'o' is a native coroutine object. Before this commit it used abc.Coroutine, and it was requested to update inspect.isgenerator(o) to use abc.Generator; it was decided, however, that inspect functions should really be tailored for checking for native types. 6. sys.set_coroutine_wrapper(w) API is updated to work with only native coroutines. Since types.coroutine decorator supports any type of callables now, it would be confusing that it does not work for all types of coroutines. 7. Exceptions logic in generators C implementation was updated to raise clearer messages for coroutines: Before: TypeError("generator raised StopIteration") After: TypeError("coroutine raised StopIteration")
2015-06-22 13:19:30 -03:00
.. versionadded:: 3.5
.. index:: statement: async def
.. _`async def`:
Coroutine function definition
-----------------------------
.. productionlist:: python-grammar
async_funcdef: [`decorators`] "async" "def" `funcname` "(" [`parameter_list`] ")"
: ["->" `expression`] ":" `suite`
.. index::
keyword: async
keyword: await
Execution of Python coroutines can be suspended and resumed at many points
(see :term:`coroutine`). :keyword:`await` expressions, :keyword:`async for` and
:keyword:`async with` can only be used in the body of a coroutine function.
Functions defined with ``async def`` syntax are always coroutine functions,
even if they do not contain ``await`` or ``async`` keywords.
It is a :exc:`SyntaxError` to use a ``yield from`` expression inside the body
of a coroutine function.
Issue #24400: Introduce a distinct type for 'async def' coroutines. Summary of changes: 1. Coroutines now have a distinct, separate from generators type at the C level: PyGen_Type, and a new typedef PyCoroObject. PyCoroObject shares the initial segment of struct layout with PyGenObject, making it possible to reuse existing generators machinery. The new type is exposed as 'types.CoroutineType'. As a consequence of having a new type, CO_GENERATOR flag is no longer applied to coroutines. 2. Having a separate type for coroutines made it possible to add an __await__ method to the type. Although it is not used by the interpreter (see details on that below), it makes coroutines naturally (without using __instancecheck__) conform to collections.abc.Coroutine and collections.abc.Awaitable ABCs. [The __instancecheck__ is still used for generator-based coroutines, as we don't want to add __await__ for generators.] 3. Add new opcode: GET_YIELD_FROM_ITER. The opcode is needed to allow passing native coroutines to the YIELD_FROM opcode. Before this change, 'yield from o' expression was compiled to: (o) GET_ITER LOAD_CONST YIELD_FROM Now, we use GET_YIELD_FROM_ITER instead of GET_ITER. The reason for adding a new opcode is that GET_ITER is used in some contexts (such as 'for .. in' loops) where passing a coroutine object is invalid. 4. Add two new introspection functions to the inspec module: getcoroutinestate(c) and getcoroutinelocals(c). 5. inspect.iscoroutine(o) is updated to test if 'o' is a native coroutine object. Before this commit it used abc.Coroutine, and it was requested to update inspect.isgenerator(o) to use abc.Generator; it was decided, however, that inspect functions should really be tailored for checking for native types. 6. sys.set_coroutine_wrapper(w) API is updated to work with only native coroutines. Since types.coroutine decorator supports any type of callables now, it would be confusing that it does not work for all types of coroutines. 7. Exceptions logic in generators C implementation was updated to raise clearer messages for coroutines: Before: TypeError("generator raised StopIteration") After: TypeError("coroutine raised StopIteration")
2015-06-22 13:19:30 -03:00
An example of a coroutine function::
async def func(param1, param2):
do_stuff()
await some_coroutine()
.. versionchanged:: 3.7
``await`` and ``async`` are now keywords; previously they were only
treated as such inside the body of a coroutine function.
.. index:: statement: async for
.. _`async for`:
The :keyword:`!async for` statement
-----------------------------------
.. productionlist:: python-grammar
async_for_stmt: "async" `for_stmt`
An :term:`asynchronous iterable` provides an ``__aiter__`` method that directly
returns an :term:`asynchronous iterator`, which can call asynchronous code in
its ``__anext__`` method.
The ``async for`` statement allows convenient iteration over asynchronous
iterables.
The following code::
async for TARGET in ITER:
SUITE
else:
SUITE2
Is semantically equivalent to::
iter = (ITER)
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iter = type(iter).__aiter__(iter)
running = True
while running:
try:
TARGET = await type(iter).__anext__(iter)
except StopAsyncIteration:
running = False
else:
SUITE
else:
SUITE2
See also :meth:`~object.__aiter__` and :meth:`~object.__anext__` for details.
It is a :exc:`SyntaxError` to use an ``async for`` statement outside the
body of a coroutine function.
.. index:: statement: async with
.. _`async with`:
The :keyword:`!async with` statement
------------------------------------
.. productionlist:: python-grammar
async_with_stmt: "async" `with_stmt`
An :term:`asynchronous context manager` is a :term:`context manager` that is
able to suspend execution in its *enter* and *exit* methods.
The following code::
async with EXPRESSION as TARGET:
SUITE
is semantically equivalent to::
manager = (EXPRESSION)
aenter = type(manager).__aenter__
aexit = type(manager).__aexit__
value = await aenter(manager)
hit_except = False
try:
TARGET = value
SUITE
except:
hit_except = True
if not await aexit(manager, *sys.exc_info()):
raise
finally:
if not hit_except:
await aexit(manager, None, None, None)
See also :meth:`~object.__aenter__` and :meth:`~object.__aexit__` for details.
It is a :exc:`SyntaxError` to use an ``async with`` statement outside the
body of a coroutine function.
.. seealso::
:pep:`492` - Coroutines with async and await syntax
The proposal that made coroutines a proper standalone concept in Python,
and added supporting syntax.
2007-08-15 11:28:22 -03:00
.. rubric:: Footnotes
.. [#] The exception is propagated to the invocation stack unless
there is a :keyword:`finally` clause which happens to raise another
exception. That new exception causes the old one to be lost.
2007-08-15 11:28:22 -03:00
.. [#] In pattern matching, a sequence is defined as one of the following:
* a class that inherits from :class:`collections.abc.Sequence`
* a Python class that has been registered as :class:`collections.abc.Sequence`
* a builtin class that has its (CPython) :data:`Py_TPFLAGS_SEQUENCE` bit set
* a class that inherits from any of the above
The following standard library classes are sequences:
* :class:`array.array`
* :class:`collections.deque`
* :class:`list`
* :class:`memoryview`
* :class:`range`
* :class:`tuple`
.. note:: Subject values of type ``str``, ``bytes``, and ``bytearray``
do not match sequence patterns.
.. [#] In pattern matching, a mapping is defined as one of the following:
* a class that inherits from :class:`collections.abc.Mapping`
* a Python class that has been registered as :class:`collections.abc.Mapping`
* a builtin class that has its (CPython) :data:`Py_TPFLAGS_MAPPING` bit set
* a class that inherits from any of the above
The standard library classes :class:`dict` and :class:`types.MappingProxyType`
are mappings.
Merged revisions 65012,65035,65037-65040,65048,65057,65077,65091-65095,65097-65099,65127-65128,65131,65133-65136,65139,65149-65151,65155,65158-65159,65176-65178,65183-65184,65187-65190,65192,65194 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r65012 | jesse.noller | 2008-07-16 15:24:06 +0200 (Wed, 16 Jul 2008) | 2 lines Apply patch for issue 3090: ARCHFLAGS parsing incorrect ........ r65035 | georg.brandl | 2008-07-16 23:19:28 +0200 (Wed, 16 Jul 2008) | 2 lines #3045: fix pydoc behavior for TEMP path with spaces. ........ r65037 | georg.brandl | 2008-07-16 23:31:41 +0200 (Wed, 16 Jul 2008) | 2 lines #1608818: errno can get set by every call to readdir(). ........ r65038 | georg.brandl | 2008-07-17 00:04:20 +0200 (Thu, 17 Jul 2008) | 2 lines #3305: self->stream can be NULL. ........ r65039 | georg.brandl | 2008-07-17 00:09:17 +0200 (Thu, 17 Jul 2008) | 2 lines #3345: fix docstring. ........ r65040 | georg.brandl | 2008-07-17 00:33:18 +0200 (Thu, 17 Jul 2008) | 2 lines #3312: fix two sqlite3 crashes. ........ r65048 | georg.brandl | 2008-07-17 01:35:54 +0200 (Thu, 17 Jul 2008) | 2 lines #3388: add a paragraph about using "with" for file objects. ........ r65057 | gregory.p.smith | 2008-07-17 05:13:05 +0200 (Thu, 17 Jul 2008) | 2 lines news note for r63052 ........ r65077 | jesse.noller | 2008-07-17 23:01:05 +0200 (Thu, 17 Jul 2008) | 3 lines Fix issue 3395, update _debugInfo to be _debug_info ........ r65091 | ronald.oussoren | 2008-07-18 07:48:03 +0200 (Fri, 18 Jul 2008) | 2 lines Last bit of a fix for issue3381 (addon for my patch in r65061) ........ r65092 | vinay.sajip | 2008-07-18 10:59:06 +0200 (Fri, 18 Jul 2008) | 1 line Issue #3389: Allow resolving dotted names for handlers in logging configuration files. Thanks to Philip Jenvey for the patch. ........ r65093 | vinay.sajip | 2008-07-18 11:00:00 +0200 (Fri, 18 Jul 2008) | 1 line Issue #3389: Allow resolving dotted names for handlers in logging configuration files. Thanks to Philip Jenvey for the patch. ........ r65094 | vinay.sajip | 2008-07-18 11:00:35 +0200 (Fri, 18 Jul 2008) | 1 line Issue #3389: Allow resolving dotted names for handlers in logging configuration files. Thanks to Philip Jenvey for the patch. ........ r65095 | vinay.sajip | 2008-07-18 11:01:10 +0200 (Fri, 18 Jul 2008) | 1 line Issue #3389: Allow resolving dotted names for handlers in logging configuration files. Thanks to Philip Jenvey for the patch. ........ r65097 | georg.brandl | 2008-07-18 12:20:59 +0200 (Fri, 18 Jul 2008) | 2 lines Remove duplicate entry in __all__. ........ r65098 | georg.brandl | 2008-07-18 12:29:30 +0200 (Fri, 18 Jul 2008) | 2 lines Correct attribute name. ........ r65099 | georg.brandl | 2008-07-18 13:15:06 +0200 (Fri, 18 Jul 2008) | 3 lines Document the different meaning of precision for {:f} and {:g}. Also document how inf and nan are formatted. #3404. ........ r65127 | raymond.hettinger | 2008-07-19 02:42:03 +0200 (Sat, 19 Jul 2008) | 1 line Improve accuracy of gamma test function ........ r65128 | raymond.hettinger | 2008-07-19 02:43:00 +0200 (Sat, 19 Jul 2008) | 1 line Add recipe to the itertools docs. ........ r65131 | georg.brandl | 2008-07-19 12:08:55 +0200 (Sat, 19 Jul 2008) | 2 lines #3378: in case of no memory, don't leak even more memory. :) ........ r65133 | georg.brandl | 2008-07-19 14:39:10 +0200 (Sat, 19 Jul 2008) | 3 lines #3302: fix segfaults when passing None for arguments that can't be NULL for the C functions. ........ r65134 | georg.brandl | 2008-07-19 14:46:12 +0200 (Sat, 19 Jul 2008) | 2 lines #3303: fix crash with invalid Py_DECREF in strcoll(). ........ r65135 | georg.brandl | 2008-07-19 15:00:22 +0200 (Sat, 19 Jul 2008) | 3 lines #3319: don't raise ZeroDivisionError if number of rounds is so low that benchtime is zero. ........ r65136 | georg.brandl | 2008-07-19 15:09:42 +0200 (Sat, 19 Jul 2008) | 3 lines #3323: mention that if inheriting from a class without __slots__, the subclass will have a __dict__ available too. ........ r65139 | georg.brandl | 2008-07-19 15:48:44 +0200 (Sat, 19 Jul 2008) | 2 lines Add ordering info for findall and finditer. ........ r65149 | raymond.hettinger | 2008-07-20 01:21:57 +0200 (Sun, 20 Jul 2008) | 1 line Fix compress() recipe in docs to use itertools. ........ r65150 | raymond.hettinger | 2008-07-20 01:58:47 +0200 (Sun, 20 Jul 2008) | 1 line Clean-up itertools docs and recipes. ........ r65151 | gregory.p.smith | 2008-07-20 02:22:08 +0200 (Sun, 20 Jul 2008) | 9 lines fix issue3120 - don't truncate handles on 64-bit Windows. This is still messy, realistically PC/_subprocess.c should never cast pointers to python numbers and back at all. I don't have a 64-bit windows build environment because microsoft apparently thinks that should cost money. Time to watch the buildbots. It builds and passes tests on 32-bit windows. ........ r65155 | georg.brandl | 2008-07-20 13:50:29 +0200 (Sun, 20 Jul 2008) | 2 lines #926501: add info where to put the docstring. ........ r65158 | neal.norwitz | 2008-07-20 21:35:23 +0200 (Sun, 20 Jul 2008) | 1 line Fix a couple of names in error messages that were wrong ........ r65159 | neal.norwitz | 2008-07-20 22:39:36 +0200 (Sun, 20 Jul 2008) | 1 line Fix misspeeld method name (negative) ........ r65176 | amaury.forgeotdarc | 2008-07-21 23:36:24 +0200 (Mon, 21 Jul 2008) | 4 lines Increment version number in NEWS file, and move items that were added after 2.6b2. (I thought there was a script to automate this kind of updates) ........ r65177 | amaury.forgeotdarc | 2008-07-22 00:00:38 +0200 (Tue, 22 Jul 2008) | 5 lines Issue2378: pdb would delete free variables when stepping into a class statement. The problem was introduced by r53954, the correction is to restore the symmetry between PyFrame_FastToLocals and PyFrame_LocalsToFast ........ r65178 | benjamin.peterson | 2008-07-22 00:05:34 +0200 (Tue, 22 Jul 2008) | 1 line don't use assert statement ........ r65183 | ronald.oussoren | 2008-07-22 09:06:00 +0200 (Tue, 22 Jul 2008) | 2 lines Fix buglet in fix for issue3381 ........ r65184 | ronald.oussoren | 2008-07-22 09:06:33 +0200 (Tue, 22 Jul 2008) | 2 lines Fix build issue on OSX 10.4, somehow this wasn't committed before. ........ r65187 | raymond.hettinger | 2008-07-22 20:54:02 +0200 (Tue, 22 Jul 2008) | 1 line Remove out-of-date section on Exact/Inexact. ........ r65188 | raymond.hettinger | 2008-07-22 21:00:47 +0200 (Tue, 22 Jul 2008) | 1 line Tuples now have both count() and index(). ........ r65189 | raymond.hettinger | 2008-07-22 21:03:05 +0200 (Tue, 22 Jul 2008) | 1 line Fix credits for math.sum() ........ r65190 | raymond.hettinger | 2008-07-22 21:18:50 +0200 (Tue, 22 Jul 2008) | 1 line One more attribution. ........ r65192 | benjamin.peterson | 2008-07-23 01:44:37 +0200 (Wed, 23 Jul 2008) | 1 line remove unneeded import ........ r65194 | benjamin.peterson | 2008-07-23 15:25:06 +0200 (Wed, 23 Jul 2008) | 1 line use isinstance ........
2008-07-23 13:10:53 -03:00
.. [#] A string literal appearing as the first statement in the function body is
transformed into the function's ``__doc__`` attribute and therefore the
function's :term:`docstring`.
.. [#] A string literal appearing as the first statement in the class body is
transformed into the namespace's ``__doc__`` item and therefore the class's
:term:`docstring`.