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Continue going through the language reference, bringing it up-to-date. 

In particular, document the new comprehensions and remove mentions of long integers.
Fix a bunch of related things in the lib ref.
This commit is contained in:
Georg Brandl 2007-09-07 14:15:41 +00:00
parent 44fa8f650f
commit 96593ed348
7 changed files with 296 additions and 280 deletions
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12
Doc/library/constants.rst
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@ -5,6 +5,11 @@ Built-in Constants
A small number of constants live in the built-in namespace. They are:
.. note::
:data:`None`, :data:`False`, :data:`True` and :data:`__debug__` cannot be
reassigned, so they can be considered "true" constants.
.. XXX False, True, None are keywords too
.. data:: False
@ -37,3 +42,10 @@ A small number of constants live in the built-in namespace. They are:
slicing syntax for user-defined container data types, as in ::
val = container[1:5, 7:10, ...]
.. data:: __debug__
A boolean value that is :data:`True` if Python was not started with the
``-O`` command line option. Its value is used indirectly by the
:keyword:`assert` statement, but it can also be used directly in code.

4
Doc/library/fileinput.rst
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@ -19,10 +19,10 @@ The typical use is::
This iterates over the lines of all files listed in ``sys.argv[1:]``, defaulting
to ``sys.stdin`` if the list is empty. If a filename is ``'-'``, it is also
replaced by ``sys.stdin``. To specify an alternative list of filenames, pass it
as the first argument to :func:`input`. A single file name is also allowed.
as the first argument to :func:`.input`. A single file name is also allowed.
All files are opened in text mode by default, but you can override this by
specifying the *mode* parameter in the call to :func:`input` or
specifying the *mode* parameter in the call to :func:`.input` or
:class:`FileInput()`. If an I/O error occurs during opening or reading a file,
:exc:`IOError` is raised.

2
Doc/library/new.rst
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@ -50,4 +50,4 @@ The :mod:`new` module defines the following functions:
This function returns a new class object, with name *name*, derived from
*baseclasses* (which should be a tuple of classes) and with namespace *dict*.
Alias for the built-in :class:`type`.

4
Doc/library/readline.rst
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@ -12,8 +12,8 @@ The :mod:`readline` module defines a number of functions to facilitate
completion and reading/writing of history files from the Python interpreter.
This module can be used directly or via the :mod:`rlcompleter` module. Settings
made using this module affect the behaviour of both the interpreter's
interactive prompt and the prompts offered by the :func:`raw_input` and
:func:`input` built-in functions.
interactive prompt and the prompts offered by the built-in :func:`input`
function.
The :mod:`readline` module defines the following functions:

69
Doc/reference/executionmodel.rst
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@ -26,17 +26,16 @@ Naming and binding
Each occurrence of a name in the program text refers to the :dfn:`binding` of
that name established in the innermost function block containing the use.
.. index:: single: block
.. index:: block
A :dfn:`block` is a piece of Python program text that is executed as a unit.
The following are blocks: a module, a function body, and a class definition.
Each command typed interactively is a block. A script file (a file given as
standard input to the interpreter or specified on the interpreter command line
the first argument) is a code block. A script command (a command specified on
the interpreter command line with the '**-c**' option) is a code block. The string
argument passed to the built-in functions :func:`eval` and :func:`exec` is a
code block. The expression read and evaluated by the built-in function
:func:`input` is a code block.
the interpreter command line with the '**-c**' option) is a code block. The
string argument passed to the built-in functions :func:`eval` and :func:`exec`
is a code block.
.. index:: pair: execution; frame
@ -44,7 +43,7 @@ A code block is executed in an :dfn:`execution frame`. A frame contains some
administrative information (used for debugging) and determines where and how
execution continues after the code block's execution has completed.
.. index:: single: scope
.. index:: scope
A :dfn:`scope` defines the visibility of a name within a block. If a local
variable is defined in a block, its scope includes that block. If the
@ -61,10 +60,11 @@ scope. The set of all such scopes visible to a code block is called the block's
.. index:: pair: free; variable
If a name is bound in a block, it is a local variable of that block. If a name
is bound at the module level, it is a global variable. (The variables of the
module code block are local and global.) If a variable is used in a code block
but not defined there, it is a :dfn:`free variable`.
If a name is bound in a block, it is a local variable of that block, unless
declared as :keyword:`nonlocal`. If a name is bound at the module level, it is
a global variable. (The variables of the module code block are local and
global.) If a variable is used in a code block but not defined there, it is a
:dfn:`free variable`.
.. index::
single: NameError (built-in exception)
@ -96,18 +96,20 @@ function definition or at the module level (the top-level code block).
If a name binding operation occurs anywhere within a code block, all uses of the
name within the block are treated as references to the current block. This can
lead to errors when a name is used within a block before it is bound. This rule
lead to errors when a name is used within a block before it is bound. This rule
is subtle. Python lacks declarations and allows name binding operations to
occur anywhere within a code block. The local variables of a code block can be
determined by scanning the entire text of the block for name binding operations.
If the global statement occurs within a block, all uses of the name specified in
the statement refer to the binding of that name in the top-level namespace.
Names are resolved in the top-level namespace by searching the global namespace,
i.e. the namespace of the module containing the code block, and the builtin
namespace, the namespace of the module :mod:`__builtin__`. The global namespace
is searched first. If the name is not found there, the builtin namespace is
searched. The global statement must precede all uses of the name.
If the :keyword:`global` statement occurs within a block, all uses of the name
specified in the statement refer to the binding of that name in the top-level
namespace. Names are resolved in the top-level namespace by searching the
global namespace, i.e. the namespace of the module containing the code block,
and the builtin namespace, the namespace of the module :mod:`__builtin__`. The
global namespace is searched first. If the name is not found there, the builtin
namespace is searched. The global statement must precede all uses of the name.
.. XXX document "nonlocal" semantics here
.. index:: pair: restricted; execution
@ -137,7 +139,7 @@ block. If the nearest enclosing scope for a free variable contains a global
statement, the free variable is treated as a global.
A class definition is an executable statement that may use and define names.
These references follow the normal rules for name resolution. The namespace of
These references follow the normal rules for name resolution. The namespace of
the class definition becomes the attribute dictionary of the class. Names
defined at the class scope are not visible in methods.
@ -157,13 +159,14 @@ If the wild card form of import --- ``import *`` --- is used in a function and
the function contains or is a nested block with free variables, the compiler
will raise a :exc:`SyntaxError`.
The :func:`eval` and :func:`exec` functions do
not have access to the full environment for resolving names. Names may be
resolved in the local and global namespaces of the caller. Free variables are
not resolved in the nearest enclosing namespace, but in the global namespace.
[#]_ The :func:`exec` and :func:`eval` functions have optional
arguments to override the global and local namespace. If only one namespace is
specified, it is used for both.
.. XXX from * also invalid with relative imports (at least currently)
The :func:`eval` and :func:`exec` functions do not have access to the full
environment for resolving names. Names may be resolved in the local and global
namespaces of the caller. Free variables are not resolved in the nearest
enclosing namespace, but in the global namespace. [#]_ The :func:`exec` and
:func:`eval` functions have optional arguments to override the global and local
namespace. If only one namespace is specified, it is used for both.
.. _exceptions:
@ -205,21 +208,17 @@ re-entering the offending piece of code from the top).
When an exception is not handled at all, the interpreter terminates execution of
the program, or returns to its interactive main loop. In either case, it prints
a stack backtrace, except when the exception is :exc:`SystemExit`.
a stack backtrace, except when the exception is :exc:`SystemExit`.
Exceptions are identified by class instances. The :keyword:`except` clause is
selected depending on the class of the instance: it must reference the class of
the instance or a base class thereof. The instance can be received by the
handler and can carry additional information about the exceptional condition.
Exceptions can also be identified by strings, in which case the
:keyword:`except` clause is selected by object identity. An arbitrary value can
be raised along with the identifying string which can be passed to the handler.
.. warning::
Messages to exceptions are not part of the Python API. Their contents may
change from one version of Python to the next without warning and should not be
Exception messages are not part of the Python API. Their contents may change
from one version of Python to the next without warning and should not be
relied on by code which will run under multiple versions of the interpreter.
See also the description of the :keyword:`try` statement in section :ref:`try`
@ -227,6 +226,6 @@ and :keyword:`raise` statement in section :ref:`raise`.
.. rubric:: Footnotes
.. [#] This limitation occurs because the code that is executed by these operations is
not available at the time the module is compiled.
.. [#] This limitation occurs because the code that is executed by these operations
is not available at the time the module is compiled.

478
Doc/reference/expressions.rst
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@ -27,25 +27,19 @@ Arithmetic conversions
.. index:: pair: arithmetic; conversion
.. XXX no coercion rules are documented anymore
When a description of an arithmetic operator below uses the phrase "the numeric
arguments are converted to a common type," the arguments are coerced using the
coercion rules. If both arguments are standard
numeric types, the following coercions are applied:
arguments are converted to a common type," this means that the operator
implementation for built-in types works that way:
* If either argument is a complex number, the other is converted to complex;
* otherwise, if either argument is a floating point number, the other is
converted to floating point;
* otherwise, if either argument is a long integer, the other is converted to
long integer;
* otherwise, both must be plain integers and no conversion is necessary.
* otherwise, both must be integers and no conversion is necessary.
Some additional rules apply for certain operators (e.g., a string left argument
to the '%' operator). Extensions can define their own coercions.
to the '%' operator). Extensions must define their own conversion behavior.
.. _atoms:
@ -53,18 +47,16 @@ to the '%' operator). Extensions can define their own coercions.
Atoms
=====
.. index:: single: atom
.. index:: atom
Atoms are the most basic elements of expressions. The simplest atoms are
identifiers or literals. Forms enclosed in reverse quotes or in parentheses,
brackets or braces are also categorized syntactically as atoms. The syntax for
atoms is:
identifiers or literals. Forms enclosed in parentheses, brackets or braces are
also categorized syntactically as atoms. The syntax for atoms is:
.. productionlist::
atom: `identifier` | `literal` | `enclosure`
enclosure: `parenth_form` | `list_display`
: | `generator_expression` | `dict_display`
: | `string_conversion` | `yield_atom`
enclosure: `parenth_form` | `list_display` | `dict_display` | `set_display`
: | `generator_expression` | `yield_atom`
.. _atom-identifiers:
@ -72,9 +64,7 @@ atoms is:
Identifiers (Names)
-------------------
.. index::
single: name
single: identifier
.. index:: name, identifier
An identifier occurring as an atom is a name. See section :ref:`identifiers`
for lexical definition and section :ref:`naming` for documentation of naming and
@ -103,9 +93,6 @@ transformed name is extremely long (longer than 255 characters), implementation
defined truncation may happen. If the class name consists only of underscores,
no transformation is done.
.. %
.. %
.. _atom-literals:
@ -114,26 +101,26 @@ Literals
.. index:: single: literal
Python supports string literals and various numeric literals:
Python supports string and bytes literals and various numeric literals:
.. productionlist::
literal: `stringliteral` | `integer` | `longinteger`
: | `floatnumber` | `imagnumber`
literal: `stringliteral` | `bytesliteral`
: | `integer` | `floatnumber` | `imagnumber`
Evaluation of a literal yields an object of the given type (string, integer,
long integer, floating point number, complex number) with the given value. The
value may be approximated in the case of floating point and imaginary (complex)
Evaluation of a literal yields an object of the given type (string, bytes,
integer, floating point number, complex number) with the given value. The value
may be approximated in the case of floating point and imaginary (complex)
literals. See section :ref:`literals` for details.
.. index::
triple: immutable; data; type
pair: immutable; object
All literals correspond to immutable data types, and hence the object's identity
is less important than its value. Multiple evaluations of literals with the
same value (either the same occurrence in the program text or a different
occurrence) may obtain the same object or a different object with the same
value.
With the exception of bytes literals, these all correspond to immutable data
types, and hence the object's identity is less important than its value.
Multiple evaluations of literals with the same value (either the same occurrence
in the program text or a different occurrence) may obtain the same object or a
different object with the same value.
.. _parenthesized:
@ -168,6 +155,35 @@ required --- allowing unparenthesized "nothing" in expressions would cause
ambiguities and allow common typos to pass uncaught.
.. _comprehensions:
Displays for lists, sets and dictionaries
-----------------------------------------
For constructing a list, a set or a dictionary Python provides special syntax
called "displays", each of them in two flavors:
* either the container contents are listed explicitly, or
* they are computed via a set of looping and filtering instructions, called a
:dfn:`comprehension`.
Common syntax elements for comprehensions are:
.. productionlist::
comprehension: `expression` `comp_for`
comp_for: "for" `target_list` "in" `or_test` [`comp_iter`]
comp_iter: `comp_for` | `comp_if`
comp_if: "if" `expression_nocond` [`comp_iter`]
The comprehension consists of a single expression followed by at least one
:keyword:`for` clause and zero or more :keyword:`for` or :keyword:`if` clauses.
In this case, the elements of the new container are those that would be produced
by considering each of the :keyword:`for` or :keyword:`if` clauses a block,
nesting from left to right, and evaluating the expression to produce an element
each time the innermost block is reached.
.. _lists:
List displays
@ -176,71 +192,41 @@ List displays
.. index::
pair: list; display
pair: list; comprehensions
pair: empty; list
object: list
A list display is a possibly empty series of expressions enclosed in square
brackets:
.. productionlist::
list_display: "[" [`expression_list` | `list_comprehension`] "]"
list_comprehension: `expression` `list_for`
list_for: "for" `target_list` "in" `old_expression_list` [`list_iter`]
old_expression_list: `old_expression` [("," `old_expression`)+ [","]]
list_iter: `list_for` | `list_if`
list_if: "if" `old_expression` [`list_iter`]
list_display: "[" [`expression_list` | `comprehension`] "]"
.. index::
pair: list; comprehensions
object: list
pair: empty; list
A list display yields a new list object. Its contents are specified by
providing either a list of expressions or a list comprehension. When a
comma-separated list of expressions is supplied, its elements are evaluated from
left to right and placed into the list object in that order. When a list
comprehension is supplied, it consists of a single expression followed by at
least one :keyword:`for` clause and zero or more :keyword:`for` or :keyword:`if`
clauses. In this case, the elements of the new list are those that would be
produced by considering each of the :keyword:`for` or :keyword:`if` clauses a
block, nesting from left to right, and evaluating the expression to produce a
list element each time the innermost block is reached [#]_.
A list display yields a new list object, the contents being specified by either
a list of expressions or a comprehension. When a comma-separated list of
expressions is supplied, its elements are evaluated from left to right and
placed into the list object in that order. When a comprehension is supplied,
the list is constructed from the elements resulting from the comprehension.
.. _genexpr:
.. _set:
Generator expressions
---------------------
Set displays
------------
.. index:: pair: generator; expression
.. index:: pair: set; display
object: set
A generator expression is a compact generator notation in parentheses:
A set display is denoted by curly braces and distinguishable from dictionary
displays by the lack of colons separating keys and values:
.. productionlist::
generator_expression: "(" `expression` `genexpr_for` ")"
genexpr_for: "for" `target_list` "in" `or_test` [`genexpr_iter`]
genexpr_iter: `genexpr_for` | `genexpr_if`
genexpr_if: "if" `old_expression` [`genexpr_iter`]
set_display: "{" [`expression_list` | `comprehension`] "}"
.. index:: object: generator
A generator expression yields a new generator object. It consists of a single
expression followed by at least one :keyword:`for` clause and zero or more
:keyword:`for` or :keyword:`if` clauses. The iterating values of the new
generator are those that would be produced by considering each of the
:keyword:`for` or :keyword:`if` clauses a block, nesting from left to right, and
evaluating the expression to yield a value that is reached the innermost block
for each iteration.
Variables used in the generator expression are evaluated lazily when the
:meth:`__next__` method is called for generator object (in the same fashion as
normal generators). However, the leftmost :keyword:`for` clause is immediately
evaluated so that error produced by it can be seen before any other possible
error in the code that handles the generator expression. Subsequent
:keyword:`for` clauses cannot be evaluated immediately since they may depend on
the previous :keyword:`for` loop. For example: ``(x*y for x in range(10) for y
in bar(x))``.
The parentheses can be omitted on calls with only one argument. See section
:ref:`calls` for the detail.
A set display yields a new mutable set object, the contents being specified by
either a sequence of expressions or a comprehension. When a comma-separated
list of expressions is supplied, its elements are evaluated from left to right
and added to the set object. When a comprehension is supplied, the set is
constructed from the elements resulting from the comprehension.
.. _dict:
@ -249,29 +235,33 @@ Dictionary displays
-------------------
.. index:: pair: dictionary; display
.. index::
single: key
single: datum
single: key/datum pair
key, datum, key/datum pair
object: dictionary
A dictionary display is a possibly empty series of key/datum pairs enclosed in
curly braces:
.. productionlist::
dict_display: "{" [`key_datum_list`] "}"
dict_display: "{" [`key_datum_list` | `dict_comprehension`] "}"
key_datum_list: `key_datum` ("," `key_datum`)* [","]
key_datum: `expression` ":" `expression`
.. index:: object: dictionary
dict_comprehension: `expression` ":" `expression` `comp_for`
A dictionary display yields a new dictionary object.
The key/datum pairs are evaluated from left to right to define the entries of
the dictionary: each key object is used as a key into the dictionary to store
the corresponding datum.
If a comma-separated sequence of key/datum pairs is given, they are evaluated
from left to right to define the entries of the dictionary: each key object is
used as a key into the dictionary to store the corresponding datum. This means
that you can specify the same key multiple times in the key/datum list, and the
final dictionary's value for that key will be the last one given.
A dict comprehension, in contrast to list and set comprehensions, needs two
expressions separated with a colon followed by the usual "for" and "if" clauses.
When the comprehension is run, the resulting key and value elements are inserted
in the new dictionary in the order they are produced.
.. index:: pair: immutable; object
hashable
Restrictions on the types of the key values are listed earlier in section
:ref:`types`. (To summarize, the key type should be hashable, which excludes
@ -280,6 +270,36 @@ datum (textually rightmost in the display) stored for a given key value
prevails.
.. _genexpr:
Generator expressions
---------------------
.. index:: pair: generator; expression
object: generator
A generator expression is a compact generator notation in parentheses:
.. productionlist::
generator_expression: "(" `expression` `comp_for` ")"
A generator expression yields a new generator object. Its syntax is the same as
for comprehensions, except that it is enclosed in parentheses instead of
brackets or curly braces.
Variables used in the generator expression are evaluated lazily when the
:meth:`__next__` method is called for generator object (in the same fashion as
normal generators). However, the leftmost :keyword:`for` clause is immediately
evaluated, so that an error produced by it can be seen before any other possible
error in the code that handles the generator expression. Subsequent
:keyword:`for` clauses cannot be evaluated immediately since they may depend on
the previous :keyword:`for` loop. For example: ``(x*y for x in range(10) for y
in bar(x))``.
The parentheses can be omitted on calls with only one argument. See section
:ref:`calls` for the detail.
.. _yieldexpr:
Yield expressions
@ -295,7 +315,7 @@ Yield expressions
yield_expression: "yield" [`expression_list`]
The :keyword:`yield` expression is only used when defining a generator function,
and can only be used in the body of a function definition. Using a
and can only be used in the body of a function definition. Using a
:keyword:`yield` expression in a function definition is sufficient to cause that
definition to create a generator function instead of a normal function.
@ -308,7 +328,7 @@ generator's caller. By suspended we mean that all local state is retained,
including the current bindings of local variables, the instruction pointer, and
the internal evaluation stack. When the execution is resumed by calling one of
the generator's methods, the function can proceed exactly as if the
:keyword:`yield` expression was just another external call. The value of the
:keyword:`yield` expression was just another external call. The value of the
:keyword:`yield` expression after resuming depends on the method which resumed
the execution.
@ -328,16 +348,19 @@ generator function:
.. index:: exception: StopIteration
.. method:: generator.next()
.. method:: generator.__next__()
Starts the execution of a generator function or resumes it at the last executed
:keyword:`yield` expression. When a generator function is resumed with a
:meth:`next` method, the current :keyword:`yield` expression always evaluates to
:const:`None`. The execution then continues to the next :keyword:`yield`
expression, where the generator is suspended again, and the value of the
:token:`expression_list` is returned to :meth:`next`'s caller. If the generator
exits without yielding another value, a :exc:`StopIteration` exception is
raised.
Starts the execution of a generator function or resumes it at the last
executed :keyword:`yield` expression. When a generator function is resumed
with a :meth:`next` method, the current :keyword:`yield` expression always
evaluates to :const:`None`. The execution then continues to the next
:keyword:`yield` expression, where the generator is suspended again, and the
value of the :token:`expression_list` is returned to :meth:`next`'s caller.
If the generator exits without yielding another value, a :exc:`StopIteration`
exception is raised.
This method is normally called implicitly, e.g. by a :keyword:`for` loop, or
by the built-in :func:`next` function.
.. method:: generator.send(value)
@ -346,8 +369,8 @@ generator function:
``value`` argument becomes the result of the current :keyword:`yield`
expression. The :meth:`send` method returns the next value yielded by the
generator, or raises :exc:`StopIteration` if the generator exits without
yielding another value. When :meth:`send` is called to start the generator, it
must be called with :const:`None` as the argument, because there is no
yielding another value. When :meth:`send` is called to start the generator,
it must be called with :const:`None` as the argument, because there is no
:keyword:`yield` expression that could receieve the value.
@ -365,12 +388,12 @@ generator function:
.. method:: generator.close()
Raises a :exc:`GeneratorExit` at the point where the generator function was
paused. If the generator function then raises :exc:`StopIteration` (by exiting
normally, or due to already being closed) or :exc:`GeneratorExit` (by not
catching the exception), close returns to its caller. If the generator yields a
value, a :exc:`RuntimeError` is raised. If the generator raises any other
exception, it is propagated to the caller. :meth:`close` does nothing if the
generator has already exited due to an exception or normal exit.
paused. If the generator function then raises :exc:`StopIteration` (by
exiting normally, or due to already being closed) or :exc:`GeneratorExit` (by
not catching the exception), close returns to its caller. If the generator
yields a value, a :exc:`RuntimeError` is raised. If the generator raises any
other exception, it is propagated to the caller. :meth:`close` does nothing
if the generator has already exited due to an exception or normal exit.
Here is a simple example that demonstrates the behavior of generators and
generator functions::
@ -390,10 +413,10 @@ generator functions::
... print("Don't forget to clean up when 'close()' is called.")
...
>>> generator = echo(1)
>>> print(generator.next())
>>> print(next(generator))
Execution starts when 'next()' is called for the first time.
1
>>> print(generator.next())
>>> print(next(generator))
None
>>> print(generator.send(2))
2
@ -406,8 +429,8 @@ generator functions::
.. seealso::
:pep:`0342` - Coroutines via Enhanced Generators
The proposal to enhance the API and syntax of generators, making them usable as
simple coroutines.
The proposal to enhance the API and syntax of generators, making them
usable as simple coroutines.
.. _primaries:
@ -442,11 +465,12 @@ An attribute reference is a primary followed by a period and a name:
object: list
The primary must evaluate to an object of a type that supports attribute
references, e.g., a module, list, or an instance. This object is then asked to
produce the attribute whose name is the identifier. If this attribute is not
available, the exception :exc:`AttributeError` is raised. Otherwise, the type
and value of the object produced is determined by the object. Multiple
evaluations of the same attribute reference may yield different objects.
references, which most objects do. This object is then asked to produce the
attribute whose name is the identifier (which can be customized by overriding
the :meth:`__getattr__` method). If this attribute is not available, the
exception :exc:`AttributeError` is raised. Otherwise, the type and value of the
object produced is determined by the object. Multiple evaluations of the same
attribute reference may yield different objects.
.. _subscriptions:
@ -471,19 +495,22 @@ A subscription selects an item of a sequence (string, tuple or list) or mapping
.. productionlist::
subscription: `primary` "[" `expression_list` "]"
The primary must evaluate to an object of a sequence or mapping type.
The primary must evaluate to an object that supports subscription, e.g. a list
or dictionary. User-defined objects can support subscription by defining a
:meth:`__getitem__` method.
For built-in objects, there are two types of objects that support subscription:
If the primary is a mapping, the expression list must evaluate to an object
whose value is one of the keys of the mapping, and the subscription selects the
value in the mapping that corresponds to that key. (The expression list is a
tuple except if it has exactly one item.)
If the primary is a sequence, the expression (list) must evaluate to a plain
integer. If this value is negative, the length of the sequence is added to it
(so that, e.g., ``x[-1]`` selects the last item of ``x``.) The resulting value
must be a nonnegative integer less than the number of items in the sequence, and
the subscription selects the item whose index is that value (counting from
zero).
If the primary is a sequence, the expression (list) must evaluate to an integer.
If this value is negative, the length of the sequence is added to it (so that,
e.g., ``x[-1]`` selects the last item of ``x``.) The resulting value must be a
nonnegative integer less than the number of items in the sequence, and the
subscription selects the item whose index is that value (counting from zero).
.. index::
single: character
@ -534,15 +561,16 @@ slice list contains no proper slice).
single: step (slice object attribute)
The semantics for a slicing are as follows. The primary must evaluate to a
mapping object, and it is indexed with a key that is constructed from the
slice list, as follows. If the slice list contains at least one comma, the
key is a tuple containing the conversion of the slice items; otherwise, the
conversion of the lone slice item is the key. The conversion of a slice
item that is an expression is that expression. The conversion of a proper
slice is a slice object (see section :ref:`types`) whose :attr:`start`,
:attr:`stop` and :attr:`step` attributes are the values of the expressions
given as lower bound, upper bound and stride, respectively, substituting
``None`` for missing expressions.
mapping object, and it is indexed (using the same :meth:`__getitem__` method as
normal subscription) with a key that is constructed from the slice list, as
follows. If the slice list contains at least one comma, the key is a tuple
containing the conversion of the slice items; otherwise, the conversion of the
lone slice item is the key. The conversion of a slice item that is an
expression is that expression. The conversion of a proper slice is a slice
object (see section :ref:`types`) whose :attr:`start`, :attr:`stop` and
:attr:`step` attributes are the values of the expressions given as lower bound,
upper bound and stride, respectively, substituting ``None`` for missing
expressions.
.. _calls:
@ -576,10 +604,11 @@ does not affect the semantics.
The primary must evaluate to a callable object (user-defined functions, built-in
functions, methods of built-in objects, class objects, methods of class
instances, and certain class instances themselves are callable; extensions may
define additional callable object types). All argument expressions are
evaluated before the call is attempted. Please refer to section :ref:`function`
for the syntax of formal parameter lists.
instances, and all objects having a :meth:`__call__` method are callable). All
argument expressions are evaluated before the call is attempted. Please refer
to section :ref:`function` for the syntax of formal parameter lists.
.. XXX update with kwonly args PEP
If keyword arguments are present, they are first converted to positional
arguments, as follows. First, a list of unfilled slots is created for the
@ -722,16 +751,12 @@ for the operands): ``-1**2`` results in ``-1``.
The power operator has the same semantics as the built-in :func:`pow` function,
when called with two arguments: it yields its left argument raised to the power
of its right argument. The numeric arguments are first converted to a common
type. The result type is that of the arguments after coercion.
type, and the result is of that type.
With mixed operand types, the coercion rules for binary arithmetic operators
apply. For int and long int operands, the result has the same type as the
operands (after coercion) unless the second argument is negative; in that case,
all arguments are converted to float and a float result is delivered. For
example, ``10**2`` returns ``100``, but ``10**-2`` returns ``0.01``. (This last
feature was added in Python 2.2. In Python 2.1 and before, if both arguments
were of integer types and the second argument was negative, an exception was
raised).
For int operands, the result has the same type as the operands unless the second
argument is negative; in that case, all arguments are converted to float and a
float result is delivered. For example, ``10**2`` returns ``100``, but
``10**-2`` returns ``0.01``.
Raising ``0.0`` to a negative power results in a :exc:`ZeroDivisionError`.
Raising a negative number to a fractional power results in a :exc:`ValueError`.
@ -763,9 +788,9 @@ The unary ``+`` (plus) operator yields its numeric argument unchanged.
.. index:: single: inversion
The unary ``~`` (invert) operator yields the bit-wise inversion of its plain or
long integer argument. The bit-wise inversion of ``x`` is defined as
``-(x+1)``. It only applies to integral numbers.
The unary ``~`` (invert) operator yields the bit-wise inversion of its integer
argument. The bit-wise inversion of ``x`` is defined as ``-(x+1)``. It only
applies to integral numbers.
.. index:: exception: TypeError
@ -793,11 +818,10 @@ operators and one for additive operators:
.. index:: single: multiplication
The ``*`` (multiplication) operator yields the product of its arguments. The
arguments must either both be numbers, or one argument must be an integer (plain
or long) and the other must be a sequence. In the former case, the numbers are
converted to a common type and then multiplied together. In the latter case,
sequence repetition is performed; a negative repetition factor yields an empty
sequence.
arguments must either both be numbers, or one argument must be an integer and
the other must be a sequence. In the former case, the numbers are converted to a
common type and then multiplied together. In the latter case, sequence
repetition is performed; a negative repetition factor yields an empty sequence.
.. index::
exception: ZeroDivisionError
@ -805,9 +829,10 @@ sequence.
The ``/`` (division) and ``//`` (floor division) operators yield the quotient of
their arguments. The numeric arguments are first converted to a common type.
Plain or long integer division yields an integer of the same type; the result is
that of mathematical division with the 'floor' function applied to the result.
Division by zero raises the :exc:`ZeroDivisionError` exception.
Integer division yields a float, while floor division of integers results in an
integer; the result is that of mathematical division with the 'floor' function
applied to the result. Division by zero raises the :exc:`ZeroDivisionError`
exception.
.. index:: single: modulo
@ -820,25 +845,23 @@ result with the same sign as its second operand (or zero); the absolute value of
the result is strictly smaller than the absolute value of the second operand
[#]_.
The integer division and modulo operators are connected by the following
identity: ``x == (x/y)*y + (x%y)``. Integer division and modulo are also
connected with the built-in function :func:`divmod`: ``divmod(x, y) == (x/y,
x%y)``. These identities don't hold for floating point numbers; there similar
identities hold approximately where ``x/y`` is replaced by ``floor(x/y)`` or
``floor(x/y) - 1`` [#]_.
The floor division and modulo operators are connected by the following
identity: ``x == (x//y)*y + (x%y)``. Floor division and modulo are also
connected with the built-in function :func:`divmod`: ``divmod(x, y) == (x//y,
x%y)``. [#]_.
In addition to performing the modulo operation on numbers, the ``%`` operator is
also overloaded by string objects to perform string formatting (also
known as interpolation). The syntax for string formatting is described in the
also overloaded by string objects to perform old-style string formatting (also
known as interpolation). The syntax for string formatting is described in the
Python Library Reference, section :ref:`old-string-formatting`.
The floor division operator, the modulo operator, and the :func:`divmod`
function are not defined for complex numbers. Instead, convert to a
floating point number using the :func:`abs` function if appropriate.
function are not defined for complex numbers. Instead, convert to a floating
point number using the :func:`abs` function if appropriate.
.. index:: single: addition
The ``+`` (addition) operator yields the sum of its arguments. The arguments
The ``+`` (addition) operator yields the sum of its arguments. The arguments
must either both be numbers or both sequences of the same type. In the former
case, the numbers are converted to a common type and then added together. In
the latter case, the sequences are concatenated.
@ -861,17 +884,13 @@ The shifting operations have lower priority than the arithmetic operations:
.. productionlist::
shift_expr: `a_expr` | `shift_expr` ( "<<" | ">>" ) `a_expr`
These operators accept plain or long integers as arguments. The arguments are
converted to a common type. They shift the first argument to the left or right
by the number of bits given by the second argument.
These operators accept integers as arguments. They shift the first argument to
the left or right by the number of bits given by the second argument.
.. index:: exception: ValueError
A right shift by *n* bits is defined as division by ``pow(2,n)``. A left shift
by *n* bits is defined as multiplication with ``pow(2,n)``; for plain integers
there is no overflow check so in that case the operation drops bits and flips
the sign if the result is not less than ``pow(2,31)`` in absolute value.
Negative shift counts raise a :exc:`ValueError` exception.
by *n* bits is defined as multiplication with ``pow(2,n)``.
.. _bitwise:
@ -890,22 +909,22 @@ Each of the three bitwise operations has a different priority level:
.. index:: pair: bit-wise; and
The ``&`` operator yields the bitwise AND of its arguments, which must be plain
or long integers. The arguments are converted to a common type.
The ``&`` operator yields the bitwise AND of its arguments, which must be
integers.
.. index::
pair: bit-wise; xor
pair: exclusive; or
The ``^`` operator yields the bitwise XOR (exclusive OR) of its arguments, which
must be plain or long integers. The arguments are converted to a common type.
must be integers.
.. index::
pair: bit-wise; or
pair: inclusive; or
The ``|`` operator yields the bitwise (inclusive) OR of its arguments, which
must be plain or long integers. The arguments are converted to a common type.
must be integers.
.. _comparisons:
@ -949,8 +968,8 @@ values of two objects. The objects need not have the same type. If both are
numbers, they are converted to a common type. Otherwise, objects of different
types *always* compare unequal, and are ordered consistently but arbitrarily.
You can control comparison behavior of objects of non-builtin types by defining
a ``__cmp__`` method or rich comparison methods like ``__gt__``, described in
section :ref:`specialnames`.
a :meth:`__cmp__` method or rich comparison methods like :meth:`__gt__`,
described in section :ref:`specialnames`.
(This unusual definition of comparison was used to simplify the definition of
operations like sorting and the :keyword:`in` and :keyword:`not in` operators.
@ -961,12 +980,12 @@ Comparison of objects of the same type depends on the type:
* Numbers are compared arithmetically.
* Bytes objects are compared lexicographically using the numeric values of
their elements.
* Bytes objects are compared lexicographically using the numeric values of their
elements.
* Strings are compared lexicographically using the numeric equivalents (the
result of the built-in function :func:`ord`) of their characters. [#]_
String and bytes object can't be compared!
result of the built-in function :func:`ord`) of their characters. [#]_ String
and bytes object can't be compared!
* Tuples and lists are compared lexicographically using comparison of
corresponding elements. This means that to compare equal, each element must
@ -975,11 +994,11 @@ Comparison of objects of the same type depends on the type:
If not equal, the sequences are ordered the same as their first differing
elements. For example, ``cmp([1,2,x], [1,2,y])`` returns the same as
``cmp(x,y)``. If the corresponding element does not exist, the shorter sequence
is ordered first (for example, ``[1,2] < [1,2,3]``).
``cmp(x,y)``. If the corresponding element does not exist, the shorter
sequence is ordered first (for example, ``[1,2] < [1,2,3]``).
* Mappings (dictionaries) compare equal if and only if their sorted (key, value)
lists compare equal. [#]_ Outcomes other than equality are resolved
* Mappings (dictionaries) compare equal if and only if their sorted ``(key,
value)`` lists compare equal. [#]_ Outcomes other than equality are resolved
consistently, but are not otherwise defined. [#]_
* Most other objects of builtin types compare unequal unless they are the same
@ -987,14 +1006,11 @@ Comparison of objects of the same type depends on the type:
another one is made arbitrarily but consistently within one execution of a
program.
The operators :keyword:`in` and :keyword:`not in` test for set membership. ``x
in s`` evaluates to true if *x* is a member of the set *s*, and false otherwise.
``x not in s`` returns the negation of ``x in s``. The set membership test has
traditionally been bound to sequences; an object is a member of a set if the set
is a sequence and contains an element equal to that object. However, it is
possible for an object to support membership tests without being a sequence. In
particular, dictionaries support membership testing as a nicer way of spelling
``key in dict``; other mapping types may follow suit.
The operators :keyword:`in` and :keyword:`not in` test for membership. ``x in
s`` evaluates to true if *x* is a member of *s*, and false otherwise. ``x not
in s`` returns the negation of ``x in s``. All built-in sequences and set types
support this as well as dictionary, for which :keyword:`in` tests whether a the
dictionary has a given key.
For the list and tuple types, ``x in y`` is true if and only if there exists an
index *i* such that ``x == y[i]`` is true.
@ -1010,7 +1026,7 @@ y`` is true if and only if ``y.__contains__(x)`` is true.
For user-defined classes which do not define :meth:`__contains__` and do define
:meth:`__getitem__`, ``x in y`` is true if and only if there is a non-negative
integer index *i* such that ``x == y[i]``, and all lower integer indices do not
raise :exc:`IndexError` exception. (If any other exception is raised, it is as
raise :exc:`IndexError` exception. (If any other exception is raised, it is as
if :keyword:`in` raised that exception).
.. index::
@ -1045,7 +1061,7 @@ Boolean operations have the lowest priority of all Python operations:
.. productionlist::
expression: `conditional_expression` | `lambda_form`
old_expression: `or_test` | `old_lambda_form`
expression_nocond: `or_test` | `lambda_form_nocond`
conditional_expression: `or_test` ["if" `or_test` "else" `expression`]
or_test: `and_test` | `or_test` "or" `and_test`
and_test: `not_test` | `and_test` "and" `not_test`
@ -1055,7 +1071,8 @@ In the context of Boolean operations, and also when expressions are used by
control flow statements, the following values are interpreted as false:
``False``, ``None``, numeric zero of all types, and empty strings and containers
(including strings, tuples, lists, dictionaries, sets and frozensets). All
other values are interpreted as true.
other values are interpreted as true. User-defined objects can customize their
truth value by providing a :meth:`__bool__` method.
.. index:: operator: not
@ -1078,7 +1095,7 @@ returned; otherwise, *y* is evaluated and the resulting value is returned.
(Note that neither :keyword:`and` nor :keyword:`or` restrict the value and type
they return to ``False`` and ``True``, but rather return the last evaluated
argument. This is sometimes useful, e.g., if ``s`` is a string that should be
argument. This is sometimes useful, e.g., if ``s`` is a string that should be
replaced by a default value if it is empty, the expression ``s or 'foo'`` yields
the desired value. Because :keyword:`not` has to invent a value anyway, it does
not bother to return a value of the same type as its argument, so e.g., ``not
@ -1097,14 +1114,14 @@ Lambdas
.. productionlist::
lambda_form: "lambda" [`parameter_list`]: `expression`
old_lambda_form: "lambda" [`parameter_list`]: `old_expression`
lambda_form_nocond: "lambda" [`parameter_list`]: `expression_nocond`
Lambda forms (lambda expressions) have the same syntactic position as
expressions. They are a shorthand to create anonymous functions; the expression
``lambda arguments: expression`` yields a function object. The unnamed object
behaves like a function object defined with ::
def name(arguments):
def <lambda>(arguments):
return expression
See section :ref:`function` for the syntax of parameter lists. Note that
@ -1145,8 +1162,8 @@ Evaluation order
.. index:: pair: evaluation; order
Python evaluates expressions from left to right. Notice that while evaluating an
assignment, the right-hand side is evaluated before the left-hand side.
Python evaluates expressions from left to right. Notice that while evaluating
an assignment, the right-hand side is evaluated before the left-hand side.
In the following lines, expressions will be evaluated in the arithmetic order of
their suffixes::
@ -1167,7 +1184,7 @@ Summary
.. index:: pair: operator; precedence
The following table summarizes the operator precedences in Python, from lowest
precedence (least binding) to highest precedence (most binding). Operators in
precedence (least binding) to highest precedence (most binding). Operators in
the same box have the same precedence. Unless the syntax is explicitly given,
operators are binary. Operators in the same box group left to right (except for
comparisons, including tests, which all have the same precedence and chain from
@ -1201,7 +1218,7 @@ groups from right to left).
+----------------------------------------------+-------------------------------------+
| ``+``, ``-`` | Addition and subtraction |
+----------------------------------------------+-------------------------------------+
| ``*``, ``/``, ``%`` | Multiplication, division, remainder |
| ``*``, ``/``, ``//``, ``%`` | Multiplication, division, remainder |
+----------------------------------------------+-------------------------------------+
| ``+x``, ``-x`` | Positive, negative |
+----------------------------------------------+-------------------------------------+
@ -1217,20 +1234,16 @@ groups from right to left).
+----------------------------------------------+-------------------------------------+
| ``f(arguments...)`` | Function call |
+----------------------------------------------+-------------------------------------+
| ``(expressions...)`` | Binding or tuple display |
| ``(expressions...)`` | Binding, tuple display, generator |
| | expressions |
+----------------------------------------------+-------------------------------------+
| ``[expressions...]`` | List display |
+----------------------------------------------+-------------------------------------+
| ``{key:datum...}`` | Dictionary display |
| ``{expressions...}`` | Dictionary or set display |
+----------------------------------------------+-------------------------------------+
.. rubric:: Footnotes
.. [#] In Python 2.3, a list comprehension "leaks" the control variables of each
``for`` it contains into the containing scope. However, this behavior is
deprecated, and relying on it will not work once this bug is fixed in a future
release
.. [#] While ``abs(x%y) < abs(y)`` is true mathematically, for floats it may not be
true numerically due to roundoff. For example, and assuming a platform on which
a Python float is an IEEE 754 double-precision number, in order that ``-1e-100 %
@ -1241,22 +1254,21 @@ groups from right to left).
is more appropriate depends on the application.
.. [#] If x is very close to an exact integer multiple of y, it's possible for
``floor(x/y)`` to be one larger than ``(x-x%y)/y`` due to rounding. In such
``x//y`` to be one larger than ``(x-x%y)//y`` due to rounding. In such
cases, Python returns the latter result, in order to preserve that
``divmod(x,y)[0] * y + x % y`` be very close to ``x``.
.. [#] While comparisons between strings make sense at the byte
level, they may be counter-intuitive to users. For example, the
strings ``"\u00C7"`` and ``"\u0327\u0043"`` compare differently,
even though they both represent the same unicode character (LATIN
CAPTITAL LETTER C WITH CEDILLA).
.. [#] While comparisons between strings make sense at the byte level, they may
be counter-intuitive to users. For example, the strings ``"\u00C7"`` and
``"\u0327\u0043"`` compare differently, even though they both represent the
same unicode character (LATIN CAPTITAL LETTER C WITH CEDILLA).
.. [#] The implementation computes this efficiently, without constructing lists or
sorting.
.. [#] The implementation computes this efficiently, without constructing lists
or sorting.
.. [#] Earlier versions of Python used lexicographic comparison of the sorted (key,
value) lists, but this was very expensive for the common case of comparing for
equality. An even earlier version of Python compared dictionaries by identity
only, but this caused surprises because people expected to be able to test a
dictionary for emptiness by comparing it to ``{}``.
value) lists, but this was very expensive for the common case of comparing
for equality. An even earlier version of Python compared dictionaries by
identity only, but this caused surprises because people expected to be able
to test a dictionary for emptiness by comparing it to ``{}``.

7
Doc/reference/toplevel_components.rst
View File

@ -106,13 +106,6 @@ string argument to :func:`eval` must have the following form:
.. productionlist::
eval_input: `expression_list` NEWLINE*
.. index:: builtin: input
The input line read by :func:`input` must have the following form:
.. productionlist::
input_input: `expression_list` NEWLINE
.. index::
object: file
single: input; raw