cpython/Doc/tutorial/modules.rst

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.. _tut-modules:
*******
Modules
*******
If you quit from the Python interpreter and enter it again, the definitions you
have made (functions and variables) are lost. Therefore, if you want to write a
somewhat longer program, you are better off using a text editor to prepare the
input for the interpreter and running it with that file as input instead. This
is known as creating a *script*. As your program gets longer, you may want to
split it into several files for easier maintenance. You may also want to use a
handy function that you've written in several programs without copying its
definition into each program.
To support this, Python has a way to put definitions in a file and use them in a
script or in an interactive instance of the interpreter. Such a file is called a
*module*; definitions from a module can be *imported* into other modules or into
the *main* module (the collection of variables that you have access to in a
script executed at the top level and in calculator mode).
A module is a file containing Python definitions and statements. The file name
is the module name with the suffix :file:`.py` appended. Within a module, the
module's name (as a string) is available as the value of the global variable
``__name__``. For instance, use your favorite text editor to create a file
called :file:`fibo.py` in the current directory with the following contents::
# Fibonacci numbers module
def fib(n): # write Fibonacci series up to n
a, b = 0, 1
while b < n:
print(b, end=' ')
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a, b = b, a+b
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print()
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def fib2(n): # return Fibonacci series up to n
result = []
a, b = 0, 1
while b < n:
result.append(b)
a, b = b, a+b
return result
Now enter the Python interpreter and import this module with the following
command::
>>> import fibo
This does not enter the names of the functions defined in ``fibo`` directly in
the current symbol table; it only enters the module name ``fibo`` there. Using
the module name you can access the functions::
>>> fibo.fib(1000)
1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987
>>> fibo.fib2(100)
[1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]
>>> fibo.__name__
'fibo'
If you intend to use a function often you can assign it to a local name::
>>> fib = fibo.fib
>>> fib(500)
1 1 2 3 5 8 13 21 34 55 89 144 233 377
.. _tut-moremodules:
More on Modules
===============
A module can contain executable statements as well as function definitions.
These statements are intended to initialize the module. They are executed only
the *first* time the module is imported somewhere. [#]_
Each module has its own private symbol table, which is used as the global symbol
table by all functions defined in the module. Thus, the author of a module can
use global variables in the module without worrying about accidental clashes
with a user's global variables. On the other hand, if you know what you are
doing you can touch a module's global variables with the same notation used to
refer to its functions, ``modname.itemname``.
Modules can import other modules. It is customary but not required to place all
:keyword:`import` statements at the beginning of a module (or script, for that
matter). The imported module names are placed in the importing module's global
symbol table.
There is a variant of the :keyword:`import` statement that imports names from a
module directly into the importing module's symbol table. For example::
>>> from fibo import fib, fib2
>>> fib(500)
1 1 2 3 5 8 13 21 34 55 89 144 233 377
This does not introduce the module name from which the imports are taken in the
local symbol table (so in the example, ``fibo`` is not defined).
There is even a variant to import all names that a module defines::
>>> from fibo import *
>>> fib(500)
1 1 2 3 5 8 13 21 34 55 89 144 233 377
This imports all names except those beginning with an underscore (``_``).
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In most cases Python programmers do not use this facility since it introduces
an unknown set of names into the interpreter, possibly hiding some things
you have already defined.
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Merged revisions 62914-62916,62918-62919,62921-62922,62924-62942,62944-62945,62947-62949 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r62914 | skip.montanaro | 2008-05-08 20:45:00 -0400 (Thu, 08 May 2008) | 4 lines Add an example about using NamedTemporaryFile() to replace mktemp(). I'm unclear whether the verbatim text should have been indented or by how much. ........ r62915 | benjamin.peterson | 2008-05-08 20:50:40 -0400 (Thu, 08 May 2008) | 2 lines reindent example ........ r62927 | georg.brandl | 2008-05-09 02:09:25 -0400 (Fri, 09 May 2008) | 2 lines #2788: add .hgignore file. ........ r62928 | georg.brandl | 2008-05-09 02:10:43 -0400 (Fri, 09 May 2008) | 2 lines #2781: fix function name. ........ r62929 | georg.brandl | 2008-05-09 02:18:27 -0400 (Fri, 09 May 2008) | 2 lines Add a sentence to basicConfig() that is in the docstring. ........ r62930 | georg.brandl | 2008-05-09 02:26:54 -0400 (Fri, 09 May 2008) | 2 lines Add another link to colorsys docs. ........ r62931 | georg.brandl | 2008-05-09 02:36:07 -0400 (Fri, 09 May 2008) | 2 lines Add Kodos as a re reference. ........ r62932 | georg.brandl | 2008-05-09 02:39:58 -0400 (Fri, 09 May 2008) | 2 lines Add a note about using reload(). ........ r62933 | andrew.kuchling | 2008-05-09 07:46:05 -0400 (Fri, 09 May 2008) | 3 lines Update planned release date. Uncomment PEP 370 section. Add some module items ........ r62934 | christian.heimes | 2008-05-09 08:19:09 -0400 (Fri, 09 May 2008) | 1 line Add --user option to build_ext ........ r62948 | mark.dickinson | 2008-05-09 13:54:23 -0400 (Fri, 09 May 2008) | 3 lines Issue #2487. math.ldexp(x, n) raised OverflowError when n was large and negative; fix to return an (appropriately signed) zero instead. ........ r62949 | martin.v.loewis | 2008-05-09 14:21:55 -0400 (Fri, 09 May 2008) | 1 line Use the CHM file name that Sphinx assigns. ........
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.. note::
For efficiency reasons, each module is only imported once per interpreter
session. Therefore, if you change your modules, you must restart the
interpreter -- or, if it's just one module you want to test interactively,
use :func:`imp.reload`, e.g. ``import imp; imp.reload(modulename)``.
Merged revisions 62914-62916,62918-62919,62921-62922,62924-62942,62944-62945,62947-62949 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r62914 | skip.montanaro | 2008-05-08 20:45:00 -0400 (Thu, 08 May 2008) | 4 lines Add an example about using NamedTemporaryFile() to replace mktemp(). I'm unclear whether the verbatim text should have been indented or by how much. ........ r62915 | benjamin.peterson | 2008-05-08 20:50:40 -0400 (Thu, 08 May 2008) | 2 lines reindent example ........ r62927 | georg.brandl | 2008-05-09 02:09:25 -0400 (Fri, 09 May 2008) | 2 lines #2788: add .hgignore file. ........ r62928 | georg.brandl | 2008-05-09 02:10:43 -0400 (Fri, 09 May 2008) | 2 lines #2781: fix function name. ........ r62929 | georg.brandl | 2008-05-09 02:18:27 -0400 (Fri, 09 May 2008) | 2 lines Add a sentence to basicConfig() that is in the docstring. ........ r62930 | georg.brandl | 2008-05-09 02:26:54 -0400 (Fri, 09 May 2008) | 2 lines Add another link to colorsys docs. ........ r62931 | georg.brandl | 2008-05-09 02:36:07 -0400 (Fri, 09 May 2008) | 2 lines Add Kodos as a re reference. ........ r62932 | georg.brandl | 2008-05-09 02:39:58 -0400 (Fri, 09 May 2008) | 2 lines Add a note about using reload(). ........ r62933 | andrew.kuchling | 2008-05-09 07:46:05 -0400 (Fri, 09 May 2008) | 3 lines Update planned release date. Uncomment PEP 370 section. Add some module items ........ r62934 | christian.heimes | 2008-05-09 08:19:09 -0400 (Fri, 09 May 2008) | 1 line Add --user option to build_ext ........ r62948 | mark.dickinson | 2008-05-09 13:54:23 -0400 (Fri, 09 May 2008) | 3 lines Issue #2487. math.ldexp(x, n) raised OverflowError when n was large and negative; fix to return an (appropriately signed) zero instead. ........ r62949 | martin.v.loewis | 2008-05-09 14:21:55 -0400 (Fri, 09 May 2008) | 1 line Use the CHM file name that Sphinx assigns. ........
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.. _tut-modulesasscripts:
Executing modules as scripts
----------------------------
When you run a Python module with ::
python fibo.py <arguments>
the code in the module will be executed, just as if you imported it, but with
the ``__name__`` set to ``"__main__"``. That means that by adding this code at
the end of your module::
if __name__ == "__main__":
import sys
fib(int(sys.argv[1]))
you can make the file usable as a script as well as an importable module,
because the code that parses the command line only runs if the module is
executed as the "main" file::
$ python fibo.py 50
1 1 2 3 5 8 13 21 34
If the module is imported, the code is not run::
>>> import fibo
>>>
This is often used either to provide a convenient user interface to a module, or
for testing purposes (running the module as a script executes a test suite).
.. _tut-searchpath:
The Module Search Path
----------------------
.. index:: triple: module; search; path
When a module named :mod:`spam` is imported, the interpreter searches for a file
named :file:`spam.py` in the current directory, and then in the list of
directories specified by the environment variable :envvar:`PYTHONPATH`. This
has the same syntax as the shell variable :envvar:`PATH`, that is, a list of
directory names. When :envvar:`PYTHONPATH` is not set, or when the file is not
found there, the search continues in an installation-dependent default path; on
Unix, this is usually :file:`.:/usr/local/lib/python`.
Actually, modules are searched in the list of directories given by the variable
``sys.path`` which is initialized from the directory containing the input script
(or the current directory), :envvar:`PYTHONPATH` and the installation- dependent
default. This allows Python programs that know what they're doing to modify or
replace the module search path. Note that because the directory containing the
script being run is on the search path, it is important that the script not have
the same name as a standard module, or Python will attempt to load the script as
a module when that module is imported. This will generally be an error. See
section :ref:`tut-standardmodules` for more information.
.. %
Do we need stuff on zip files etc. ? DUBOIS
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"Compiled" Python files
-----------------------
As an important speed-up of the start-up time for short programs that use a lot
of standard modules, if a file called :file:`spam.pyc` exists in the directory
where :file:`spam.py` is found, this is assumed to contain an
already-"byte-compiled" version of the module :mod:`spam`. The modification time
of the version of :file:`spam.py` used to create :file:`spam.pyc` is recorded in
:file:`spam.pyc`, and the :file:`.pyc` file is ignored if these don't match.
Normally, you don't need to do anything to create the :file:`spam.pyc` file.
Whenever :file:`spam.py` is successfully compiled, an attempt is made to write
the compiled version to :file:`spam.pyc`. It is not an error if this attempt
fails; if for any reason the file is not written completely, the resulting
:file:`spam.pyc` file will be recognized as invalid and thus ignored later. The
contents of the :file:`spam.pyc` file are platform independent, so a Python
module directory can be shared by machines of different architectures.
Some tips for experts:
* When the Python interpreter is invoked with the :option:`-O` flag, optimized
code is generated and stored in :file:`.pyo` files. The optimizer currently
doesn't help much; it only removes :keyword:`assert` statements. When
#1370: Finish the merge r58749, log below, by resolving all conflicts in Doc/. Merged revisions 58221-58741 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r58221 | georg.brandl | 2007-09-20 10:57:59 -0700 (Thu, 20 Sep 2007) | 2 lines Patch #1181: add os.environ.clear() method. ........ r58225 | sean.reifschneider | 2007-09-20 23:33:28 -0700 (Thu, 20 Sep 2007) | 3 lines Issue1704287: "make install" fails unless you do "make" first. Make oldsharedmods and sharedmods in "libinstall". ........ r58232 | guido.van.rossum | 2007-09-22 13:18:03 -0700 (Sat, 22 Sep 2007) | 4 lines Patch # 188 by Philip Jenvey. Make tell() mark CRLF as a newline. With unit test. ........ r58242 | georg.brandl | 2007-09-24 10:55:47 -0700 (Mon, 24 Sep 2007) | 2 lines Fix typo and double word. ........ r58245 | georg.brandl | 2007-09-24 10:59:28 -0700 (Mon, 24 Sep 2007) | 2 lines #1196: document default radix for int(). ........ r58247 | georg.brandl | 2007-09-24 11:08:24 -0700 (Mon, 24 Sep 2007) | 2 lines #1177: accept 2xx responses for https too, not only http. ........ r58249 | andrew.kuchling | 2007-09-24 16:45:51 -0700 (Mon, 24 Sep 2007) | 1 line Remove stray odd character; grammar fix ........ r58250 | andrew.kuchling | 2007-09-24 16:46:28 -0700 (Mon, 24 Sep 2007) | 1 line Typo fix ........ r58251 | andrew.kuchling | 2007-09-24 17:09:42 -0700 (Mon, 24 Sep 2007) | 1 line Add various items ........ r58268 | vinay.sajip | 2007-09-26 22:34:45 -0700 (Wed, 26 Sep 2007) | 1 line Change to flush and close logic to fix #1760556. ........ r58269 | vinay.sajip | 2007-09-26 22:38:51 -0700 (Wed, 26 Sep 2007) | 1 line Change to basicConfig() to fix #1021. ........ r58270 | georg.brandl | 2007-09-26 23:26:58 -0700 (Wed, 26 Sep 2007) | 2 lines #1208: document match object's boolean value. ........ r58271 | vinay.sajip | 2007-09-26 23:56:13 -0700 (Wed, 26 Sep 2007) | 1 line Minor date change. ........ r58272 | vinay.sajip | 2007-09-27 00:35:10 -0700 (Thu, 27 Sep 2007) | 1 line Change to LogRecord.__init__() to fix #1206. Note that archaic use of type(x) == types.DictType is because of keeping 1.5.2 compatibility. While this is much less relevant these days, there probably needs to be a separate commit for removing all archaic constructs at the same time. ........ r58288 | brett.cannon | 2007-09-30 12:45:10 -0700 (Sun, 30 Sep 2007) | 9 lines tuple.__repr__ did not consider a reference loop as it is not possible from Python code; but it is possible from C. object.__str__ had the issue of not expecting a type to doing something within it's tp_str implementation that could trigger an infinite recursion, but it could in C code.. Both found thanks to BaseException and how it handles its repr. Closes issue #1686386. Thanks to Thomas Herve for taking an initial stab at coming up with a solution. ........ r58289 | brett.cannon | 2007-09-30 13:37:19 -0700 (Sun, 30 Sep 2007) | 3 lines Fix error introduced by r58288; if a tuple is length 0 return its repr and don't worry about any self-referring tuples. ........ r58294 | facundo.batista | 2007-10-02 10:01:24 -0700 (Tue, 02 Oct 2007) | 11 lines Made the various is_* operations return booleans. This was discussed with Cawlishaw by mail, and he basically confirmed that to these is_* operations, there's no need to return Decimal(0) and Decimal(1) if the language supports the False and True booleans. Also added a few tests for the these functions in extra.decTest, since they are mostly untested (apart from the doctests). Thanks Mark Dickinson ........ r58295 | facundo.batista | 2007-10-02 11:21:18 -0700 (Tue, 02 Oct 2007) | 4 lines Added a class to store the digits of log(10), so that they can be made available when necessary without recomputing. Thanks Mark Dickinson ........ r58299 | mark.summerfield | 2007-10-03 01:53:21 -0700 (Wed, 03 Oct 2007) | 4 lines Added note in footnote about string comparisons about unicodedata.normalize(). ........ r58304 | raymond.hettinger | 2007-10-03 14:18:11 -0700 (Wed, 03 Oct 2007) | 1 line enumerate() is no longer bounded to using sequences shorter than LONG_MAX. The possibility of overflow was sending some newsgroup posters into a tizzy. ........ r58305 | raymond.hettinger | 2007-10-03 17:20:27 -0700 (Wed, 03 Oct 2007) | 1 line itertools.count() no longer limited to sys.maxint. ........ r58306 | kurt.kaiser | 2007-10-03 18:49:54 -0700 (Wed, 03 Oct 2007) | 3 lines Assume that the user knows when he wants to end the line; don't insert something he didn't select or complete. ........ r58307 | kurt.kaiser | 2007-10-03 19:07:50 -0700 (Wed, 03 Oct 2007) | 2 lines Remove unused theme that was causing a fault in p3k. ........ r58308 | kurt.kaiser | 2007-10-03 19:09:17 -0700 (Wed, 03 Oct 2007) | 2 lines Clean up EditorWindow close. ........ r58309 | kurt.kaiser | 2007-10-03 19:53:07 -0700 (Wed, 03 Oct 2007) | 7 lines textView cleanup. Patch 1718043 Tal Einat. M idlelib/EditorWindow.py M idlelib/aboutDialog.py M idlelib/textView.py M idlelib/NEWS.txt ........ r58310 | kurt.kaiser | 2007-10-03 20:11:12 -0700 (Wed, 03 Oct 2007) | 3 lines configDialog cleanup. Patch 1730217 Tal Einat. ........ r58311 | neal.norwitz | 2007-10-03 23:00:48 -0700 (Wed, 03 Oct 2007) | 4 lines Coverity #151: Remove deadcode. All this code already exists above starting at line 653. ........ r58325 | fred.drake | 2007-10-04 19:46:12 -0700 (Thu, 04 Oct 2007) | 1 line wrap lines to <80 characters before fixing errors ........ r58326 | raymond.hettinger | 2007-10-04 19:47:07 -0700 (Thu, 04 Oct 2007) | 6 lines Add __asdict__() to NamedTuple and refine the docs. Add maxlen support to deque() and fixup docs. Partially fix __reduce__(). The None as a third arg was no longer supported. Still needs work on __reduce__() to handle recursive inputs. ........ r58327 | fred.drake | 2007-10-04 19:48:32 -0700 (Thu, 04 Oct 2007) | 3 lines move descriptions of ac_(in|out)_buffer_size to the right place http://bugs.python.org/issue1053 ........ r58329 | neal.norwitz | 2007-10-04 20:39:17 -0700 (Thu, 04 Oct 2007) | 3 lines dict could be NULL, so we need to XDECREF. Fix a compiler warning about passing a PyTypeObject* instead of PyObject*. ........ r58330 | neal.norwitz | 2007-10-04 20:41:19 -0700 (Thu, 04 Oct 2007) | 2 lines Fix Coverity #158: Check the correct variable. ........ r58332 | neal.norwitz | 2007-10-04 22:01:38 -0700 (Thu, 04 Oct 2007) | 7 lines Fix Coverity #159. This code was broken if save() returned a negative number since i contained a boolean value and then we compared i < 0 which should never be true. Will backport (assuming it's necessary) ........ r58334 | neal.norwitz | 2007-10-04 22:29:17 -0700 (Thu, 04 Oct 2007) | 1 line Add a note about fixing some more warnings found by Coverity. ........ r58338 | raymond.hettinger | 2007-10-05 12:07:31 -0700 (Fri, 05 Oct 2007) | 1 line Restore BEGIN/END THREADS macros which were squashed in the previous checkin ........ r58343 | gregory.p.smith | 2007-10-06 00:48:10 -0700 (Sat, 06 Oct 2007) | 3 lines Stab in the dark attempt to fix the test_bsddb3 failure on sparc and S-390 ubuntu buildbots. ........ r58344 | gregory.p.smith | 2007-10-06 00:51:59 -0700 (Sat, 06 Oct 2007) | 2 lines Allows BerkeleyDB 4.6.x >= 4.6.21 for the bsddb module. ........ r58348 | gregory.p.smith | 2007-10-06 08:47:37 -0700 (Sat, 06 Oct 2007) | 3 lines Use the host the author likely meant in the first place. pop.gmail.com is reliable. gmail.org is someones personal domain. ........ r58351 | neal.norwitz | 2007-10-06 12:16:28 -0700 (Sat, 06 Oct 2007) | 3 lines Ensure that this test will pass even if another test left an unwritable TESTFN. Also use the safe unlink in test_support instead of rolling our own here. ........ r58368 | georg.brandl | 2007-10-08 00:50:24 -0700 (Mon, 08 Oct 2007) | 3 lines #1123: fix the docs for the str.split(None, sep) case. Also expand a few other methods' docs, which had more info in the deprecated string module docs. ........ r58369 | georg.brandl | 2007-10-08 01:06:05 -0700 (Mon, 08 Oct 2007) | 2 lines Update docstring of sched, also remove an unused assignment. ........ r58370 | raymond.hettinger | 2007-10-08 02:14:28 -0700 (Mon, 08 Oct 2007) | 5 lines Add comments to NamedTuple code. Let the field spec be either a string or a non-string sequence (suggested by Martin Blais with use cases). Improve the error message in the case of a SyntaxError (caused by a duplicate field name). ........ r58371 | raymond.hettinger | 2007-10-08 02:56:29 -0700 (Mon, 08 Oct 2007) | 1 line Missed a line in the docs ........ r58372 | raymond.hettinger | 2007-10-08 03:11:51 -0700 (Mon, 08 Oct 2007) | 1 line Better variable names ........ r58376 | georg.brandl | 2007-10-08 07:12:47 -0700 (Mon, 08 Oct 2007) | 3 lines #1199: docs for tp_as_{number,sequence,mapping}, by Amaury Forgeot d'Arc. No need to merge this to py3k! ........ r58380 | raymond.hettinger | 2007-10-08 14:26:58 -0700 (Mon, 08 Oct 2007) | 1 line Eliminate camelcase function name ........ r58381 | andrew.kuchling | 2007-10-08 16:23:03 -0700 (Mon, 08 Oct 2007) | 1 line Eliminate camelcase function name ........ r58382 | raymond.hettinger | 2007-10-08 18:36:23 -0700 (Mon, 08 Oct 2007) | 1 line Make the error messages more specific ........ r58384 | gregory.p.smith | 2007-10-08 23:02:21 -0700 (Mon, 08 Oct 2007) | 10 lines Splits Modules/_bsddb.c up into bsddb.h and _bsddb.c and adds a C API object available as bsddb.db.api. This is based on the patch submitted by Duncan Grisby here: http://sourceforge.net/tracker/index.php?func=detail&aid=1551895&group_id=13900&atid=313900 See this thread for additional info: http://sourceforge.net/mailarchive/forum.php?thread_name=E1GAVDK-0002rk-Iw%40apasphere.com&forum_name=pybsddb-users It also cleans up the code a little by removing some ifdef/endifs for python prior to 2.1 and for unsupported Berkeley DB <= 3.2. ........ r58385 | gregory.p.smith | 2007-10-08 23:50:43 -0700 (Mon, 08 Oct 2007) | 5 lines Fix a double free when positioning a database cursor to a non-existant string key (and probably a few other situations with string keys). This was reported with a patch as pybsddb sourceforge bug 1708868 by jjjhhhlll at gmail. ........ r58386 | gregory.p.smith | 2007-10-09 00:19:11 -0700 (Tue, 09 Oct 2007) | 3 lines Use the highest cPickle protocol in bsddb.dbshelve. This comes from sourceforge pybsddb patch 1551443 by w_barnes. ........ r58394 | gregory.p.smith | 2007-10-09 11:26:02 -0700 (Tue, 09 Oct 2007) | 2 lines remove another sleepycat reference ........ r58396 | kurt.kaiser | 2007-10-09 12:31:30 -0700 (Tue, 09 Oct 2007) | 3 lines Allow interrupt only when executing user code in subprocess Patch 1225 Tal Einat modified from IDLE-Spoon. ........ r58399 | brett.cannon | 2007-10-09 17:07:50 -0700 (Tue, 09 Oct 2007) | 5 lines Remove file-level typedefs that were inconsistently used throughout the file. Just move over to the public API names. Closes issue1238. ........ r58401 | raymond.hettinger | 2007-10-09 17:26:46 -0700 (Tue, 09 Oct 2007) | 1 line Accept Jim Jewett's api suggestion to use None instead of -1 to indicate unbounded deques. ........ r58403 | kurt.kaiser | 2007-10-09 17:55:40 -0700 (Tue, 09 Oct 2007) | 2 lines Allow cursor color change w/o restart. Patch 1725576 Tal Einat. ........ r58404 | kurt.kaiser | 2007-10-09 18:06:47 -0700 (Tue, 09 Oct 2007) | 2 lines show paste if > 80 columns. Patch 1659326 Tal Einat. ........ r58415 | thomas.heller | 2007-10-11 12:51:32 -0700 (Thu, 11 Oct 2007) | 5 lines On OS X, use os.uname() instead of gestalt.sysv(...) to get the operating system version. This allows to use ctypes when Python was configured with --disable-toolbox-glue. ........ r58419 | neal.norwitz | 2007-10-11 20:01:01 -0700 (Thu, 11 Oct 2007) | 1 line Get rid of warning about not being able to create an existing directory. ........ r58420 | neal.norwitz | 2007-10-11 20:01:30 -0700 (Thu, 11 Oct 2007) | 1 line Get rid of warnings on a bunch of platforms by using a proper prototype. ........ r58421 | neal.norwitz | 2007-10-11 20:01:54 -0700 (Thu, 11 Oct 2007) | 4 lines Get rid of compiler warning about retval being used (returned) without being initialized. (gcc warning and Coverity 202) ........ r58422 | neal.norwitz | 2007-10-11 20:03:23 -0700 (Thu, 11 Oct 2007) | 1 line Fix Coverity 168: Close the file before returning (exiting). ........ r58423 | neal.norwitz | 2007-10-11 20:04:18 -0700 (Thu, 11 Oct 2007) | 4 lines Fix Coverity 180: Don't overallocate. We don't need structs, but pointers. Also fix a memory leak. ........ r58424 | neal.norwitz | 2007-10-11 20:05:19 -0700 (Thu, 11 Oct 2007) | 5 lines Fix Coverity 185-186: If the passed in FILE is NULL, uninitialized memory would be accessed. Will backport. ........ r58425 | neal.norwitz | 2007-10-11 20:52:34 -0700 (Thu, 11 Oct 2007) | 1 line Get this module to compile with bsddb versions prior to 4.3 ........ r58430 | martin.v.loewis | 2007-10-12 01:56:52 -0700 (Fri, 12 Oct 2007) | 3 lines Bug #1216: Restore support for Visual Studio 2002. Will backport to 2.5. ........ r58433 | raymond.hettinger | 2007-10-12 10:53:11 -0700 (Fri, 12 Oct 2007) | 1 line Fix test of count.__repr__() to ignore the 'L' if the count is a long ........ r58434 | gregory.p.smith | 2007-10-12 11:44:06 -0700 (Fri, 12 Oct 2007) | 4 lines Fixes http://bugs.python.org/issue1233 - bsddb.dbshelve.DBShelf.append was useless due to inverted logic. Also adds a test case for RECNO dbs to test_dbshelve. ........ r58445 | georg.brandl | 2007-10-13 06:20:03 -0700 (Sat, 13 Oct 2007) | 2 lines Fix email example. ........ r58450 | gregory.p.smith | 2007-10-13 16:02:05 -0700 (Sat, 13 Oct 2007) | 2 lines Fix an uncollectable reference leak in bsddb.db.DBShelf.append ........ r58453 | neal.norwitz | 2007-10-13 17:18:40 -0700 (Sat, 13 Oct 2007) | 8 lines Let the O/S supply a port if none of the default ports can be used. This should make the tests more robust at the expense of allowing tests to be sloppier by not requiring them to cleanup after themselves. (It will legitamitely help when running two test suites simultaneously or if another process is already using one of the predefined ports.) Also simplifies (slightLy) the exception handling elsewhere. ........ r58459 | neal.norwitz | 2007-10-14 11:30:21 -0700 (Sun, 14 Oct 2007) | 2 lines Don't raise a string exception, they don't work anymore. ........ r58460 | neal.norwitz | 2007-10-14 11:40:37 -0700 (Sun, 14 Oct 2007) | 1 line Use unittest for assertions ........ r58468 | armin.rigo | 2007-10-15 00:48:35 -0700 (Mon, 15 Oct 2007) | 2 lines test_bigbits was not testing what it seemed to. ........ r58471 | guido.van.rossum | 2007-10-15 08:54:11 -0700 (Mon, 15 Oct 2007) | 3 lines Change a PyErr_Print() into a PyErr_Clear(), per discussion in issue 1031213. ........ r58500 | raymond.hettinger | 2007-10-16 12:18:30 -0700 (Tue, 16 Oct 2007) | 1 line Improve error messages ........ r58506 | raymond.hettinger | 2007-10-16 14:28:32 -0700 (Tue, 16 Oct 2007) | 1 line More docs, error messages, and tests ........ r58507 | andrew.kuchling | 2007-10-16 15:58:03 -0700 (Tue, 16 Oct 2007) | 1 line Add items ........ r58508 | brett.cannon | 2007-10-16 16:24:06 -0700 (Tue, 16 Oct 2007) | 3 lines Remove ``:const:`` notation on None in parameter list. Since the markup is not rendered for parameters it just showed up as ``:const:`None` `` in the output. ........ r58509 | brett.cannon | 2007-10-16 16:26:45 -0700 (Tue, 16 Oct 2007) | 3 lines Re-order some functions whose parameters differ between PyObject and const char * so that they are next to each other. ........ r58522 | armin.rigo | 2007-10-17 11:46:37 -0700 (Wed, 17 Oct 2007) | 5 lines Fix the overflow checking of list_repeat. Introduce overflow checking into list_inplace_repeat. Backport candidate, possibly. ........ r58530 | facundo.batista | 2007-10-17 20:16:03 -0700 (Wed, 17 Oct 2007) | 7 lines Issue #1580738. When HTTPConnection reads the whole stream with read(), it closes itself. When the stream is read in several calls to read(n), it should behave in the same way if HTTPConnection knows where the end of the stream is (through self.length). Added a test case for this behaviour. ........ r58531 | facundo.batista | 2007-10-17 20:44:48 -0700 (Wed, 17 Oct 2007) | 3 lines Issue 1289, just a typo. ........ r58532 | gregory.p.smith | 2007-10-18 00:56:54 -0700 (Thu, 18 Oct 2007) | 4 lines cleanup test_dbtables to use mkdtemp. cleanup dbtables to pass txn as a keyword argument whenever possible to avoid bugs and confusion. (dbtables.py line 447 self.db.get using txn as a non-keyword was an actual bug due to this) ........ r58533 | gregory.p.smith | 2007-10-18 01:34:20 -0700 (Thu, 18 Oct 2007) | 4 lines Fix a weird bug in dbtables: if it chose a random rowid string that contained NULL bytes it would cause the database all sorts of problems in the future leading to very strange random failures and corrupt dbtables.bsdTableDb dbs. ........ r58534 | gregory.p.smith | 2007-10-18 09:32:02 -0700 (Thu, 18 Oct 2007) | 3 lines A cleaner fix than the one committed last night. Generate random rowids that do not contain null bytes. ........ r58537 | gregory.p.smith | 2007-10-18 10:17:57 -0700 (Thu, 18 Oct 2007) | 2 lines mention bsddb fixes. ........ r58538 | raymond.hettinger | 2007-10-18 14:13:06 -0700 (Thu, 18 Oct 2007) | 1 line Remove useless warning ........ r58539 | gregory.p.smith | 2007-10-19 00:31:20 -0700 (Fri, 19 Oct 2007) | 2 lines squelch the warning that this test is supposed to trigger. ........ r58542 | georg.brandl | 2007-10-19 05:32:39 -0700 (Fri, 19 Oct 2007) | 2 lines Clarify wording for apply(). ........ r58544 | mark.summerfield | 2007-10-19 05:48:17 -0700 (Fri, 19 Oct 2007) | 3 lines Added a cross-ref to each other. ........ r58545 | georg.brandl | 2007-10-19 10:38:49 -0700 (Fri, 19 Oct 2007) | 2 lines #1284: "S" means "seen", not unread. ........ r58548 | thomas.heller | 2007-10-19 11:11:41 -0700 (Fri, 19 Oct 2007) | 4 lines Fix ctypes on 32-bit systems when Python is configured --with-system-ffi. See also https://bugs.launchpad.net/bugs/72505. Ported from release25-maint branch. ........ r58550 | facundo.batista | 2007-10-19 12:25:57 -0700 (Fri, 19 Oct 2007) | 8 lines The constructor from tuple was way too permissive: it allowed bad coefficient numbers, floats in the sign, and other details that generated directly the wrong number in the best case, or triggered misfunctionality in the alorithms. Test cases added for these issues. Thanks Mark Dickinson. ........ r58559 | georg.brandl | 2007-10-20 06:22:53 -0700 (Sat, 20 Oct 2007) | 2 lines Fix code being interpreted as a target. ........ r58561 | georg.brandl | 2007-10-20 06:36:24 -0700 (Sat, 20 Oct 2007) | 2 lines Document new "cmdoption" directive. ........ r58562 | georg.brandl | 2007-10-20 08:21:22 -0700 (Sat, 20 Oct 2007) | 2 lines Make a path more Unix-standardy. ........ r58564 | georg.brandl | 2007-10-20 10:51:39 -0700 (Sat, 20 Oct 2007) | 2 lines Document new directive "envvar". ........ r58567 | georg.brandl | 2007-10-20 11:08:14 -0700 (Sat, 20 Oct 2007) | 6 lines * Add new toplevel chapter, "Using Python." (how to install, configure and setup python on different platforms -- at least in theory.) * Move the Python on Mac docs in that chapter. * Add a new chapter about the command line invocation, by stargaming. ........ r58568 | georg.brandl | 2007-10-20 11:33:20 -0700 (Sat, 20 Oct 2007) | 2 lines Change title, for now. ........ r58569 | georg.brandl | 2007-10-20 11:39:25 -0700 (Sat, 20 Oct 2007) | 2 lines Add entry to ACKS. ........ r58570 | georg.brandl | 2007-10-20 12:05:45 -0700 (Sat, 20 Oct 2007) | 2 lines Clarify -E docs. ........ r58571 | georg.brandl | 2007-10-20 12:08:36 -0700 (Sat, 20 Oct 2007) | 2 lines Even more clarification. ........ r58572 | andrew.kuchling | 2007-10-20 12:25:37 -0700 (Sat, 20 Oct 2007) | 1 line Fix protocol name ........ r58573 | andrew.kuchling | 2007-10-20 12:35:18 -0700 (Sat, 20 Oct 2007) | 1 line Various items ........ r58574 | andrew.kuchling | 2007-10-20 12:39:35 -0700 (Sat, 20 Oct 2007) | 1 line Use correct header line ........ r58576 | armin.rigo | 2007-10-21 02:14:15 -0700 (Sun, 21 Oct 2007) | 3 lines Add a crasher for the long-standing issue with closing a file while another thread uses it. ........ r58577 | georg.brandl | 2007-10-21 03:01:56 -0700 (Sun, 21 Oct 2007) | 2 lines Remove duplicate crasher. ........ r58578 | georg.brandl | 2007-10-21 03:24:20 -0700 (Sun, 21 Oct 2007) | 2 lines Unify "byte code" to "bytecode". Also sprinkle :term: markup for it. ........ r58579 | georg.brandl | 2007-10-21 03:32:54 -0700 (Sun, 21 Oct 2007) | 2 lines Add markup to new function descriptions. ........ r58580 | georg.brandl | 2007-10-21 03:45:46 -0700 (Sun, 21 Oct 2007) | 2 lines Add :term:s for descriptors. ........ r58581 | georg.brandl | 2007-10-21 03:46:24 -0700 (Sun, 21 Oct 2007) | 2 lines Unify "file-descriptor" to "file descriptor". ........ r58582 | georg.brandl | 2007-10-21 03:52:38 -0700 (Sun, 21 Oct 2007) | 2 lines Add :term: for generators. ........ r58583 | georg.brandl | 2007-10-21 05:10:28 -0700 (Sun, 21 Oct 2007) | 2 lines Add :term:s for iterator. ........ r58584 | georg.brandl | 2007-10-21 05:15:05 -0700 (Sun, 21 Oct 2007) | 2 lines Add :term:s for "new-style class". ........ r58588 | neal.norwitz | 2007-10-21 21:47:54 -0700 (Sun, 21 Oct 2007) | 1 line Add Chris Monson so he can edit PEPs. ........ r58594 | guido.van.rossum | 2007-10-22 09:27:19 -0700 (Mon, 22 Oct 2007) | 4 lines Issue #1307, patch by Derek Shockey. When "MAIL" is received without args, an exception happens instead of sending a 501 syntax error response. ........ r58598 | travis.oliphant | 2007-10-22 19:40:56 -0700 (Mon, 22 Oct 2007) | 1 line Add phuang patch from Issue 708374 which adds offset parameter to mmap module. ........ r58601 | neal.norwitz | 2007-10-22 22:44:27 -0700 (Mon, 22 Oct 2007) | 2 lines Bug #1313, fix typo (wrong variable name) in example. ........ r58609 | georg.brandl | 2007-10-23 11:21:35 -0700 (Tue, 23 Oct 2007) | 2 lines Update Pygments version from externals. ........ r58618 | guido.van.rossum | 2007-10-23 12:25:41 -0700 (Tue, 23 Oct 2007) | 3 lines Issue 1307 by Derek Shockey, fox the same bug for RCPT. Neal: please backport! ........ r58620 | raymond.hettinger | 2007-10-23 13:37:41 -0700 (Tue, 23 Oct 2007) | 1 line Shorter name for namedtuple() ........ r58621 | andrew.kuchling | 2007-10-23 13:55:47 -0700 (Tue, 23 Oct 2007) | 1 line Update name ........ r58622 | raymond.hettinger | 2007-10-23 14:23:07 -0700 (Tue, 23 Oct 2007) | 1 line Fixup news entry ........ r58623 | raymond.hettinger | 2007-10-23 18:28:33 -0700 (Tue, 23 Oct 2007) | 1 line Optimize sum() for integer and float inputs. ........ r58624 | raymond.hettinger | 2007-10-23 19:05:51 -0700 (Tue, 23 Oct 2007) | 1 line Fixup error return and add support for intermixed ints and floats/ ........ r58628 | vinay.sajip | 2007-10-24 03:47:06 -0700 (Wed, 24 Oct 2007) | 1 line Bug #1321: Fixed logic error in TimedRotatingFileHandler.__init__() ........ r58641 | facundo.batista | 2007-10-24 12:11:08 -0700 (Wed, 24 Oct 2007) | 4 lines Issue 1290. CharacterData.__repr__ was constructing a string in response that keeped having a non-ascii character. ........ r58643 | thomas.heller | 2007-10-24 12:50:45 -0700 (Wed, 24 Oct 2007) | 1 line Added unittest for calling a function with paramflags (backport from py3k branch). ........ r58645 | matthias.klose | 2007-10-24 13:00:44 -0700 (Wed, 24 Oct 2007) | 2 lines - Build using system ffi library on arm*-linux*. ........ r58651 | georg.brandl | 2007-10-24 14:40:38 -0700 (Wed, 24 Oct 2007) | 2 lines Bug #1287: make os.environ.pop() work as expected. ........ r58652 | raymond.hettinger | 2007-10-24 19:26:58 -0700 (Wed, 24 Oct 2007) | 1 line Missing DECREFs ........ r58653 | matthias.klose | 2007-10-24 23:37:24 -0700 (Wed, 24 Oct 2007) | 2 lines - Build using system ffi library on arm*-linux*, pass --with-system-ffi to CONFIG_ARGS ........ r58655 | thomas.heller | 2007-10-25 12:47:32 -0700 (Thu, 25 Oct 2007) | 2 lines ffi_type_longdouble may be already #defined. See issue 1324. ........ r58656 | kurt.kaiser | 2007-10-25 15:43:45 -0700 (Thu, 25 Oct 2007) | 3 lines Correct an ancient bug in an unused path by removing that path: register() is now idempotent. ........ r58660 | kurt.kaiser | 2007-10-25 17:10:09 -0700 (Thu, 25 Oct 2007) | 4 lines 1. Add comments to provide top-level documentation. 2. Refactor to use more descriptive names. 3. Enhance tests in main(). ........ r58675 | georg.brandl | 2007-10-26 11:30:41 -0700 (Fri, 26 Oct 2007) | 2 lines Fix new pop() method on os.environ on ignorecase-platforms. ........ r58696 | neal.norwitz | 2007-10-27 15:32:21 -0700 (Sat, 27 Oct 2007) | 1 line Update URL for Pygments. 0.8.1 is no longer available ........ r58697 | hyeshik.chang | 2007-10-28 04:19:02 -0700 (Sun, 28 Oct 2007) | 3 lines - Add support for FreeBSD 8 which is recently forked from FreeBSD 7. - Regenerate IN module for most recent maintenance tree of FreeBSD 6 and 7. ........ r58698 | hyeshik.chang | 2007-10-28 05:38:09 -0700 (Sun, 28 Oct 2007) | 2 lines Enable platform-specific tweaks for FreeBSD 8 (exactly same to FreeBSD 7's yet) ........ r58700 | kurt.kaiser | 2007-10-28 12:03:59 -0700 (Sun, 28 Oct 2007) | 2 lines Add confirmation dialog before printing. Patch 1717170 Tal Einat. ........ r58706 | guido.van.rossum | 2007-10-29 13:52:45 -0700 (Mon, 29 Oct 2007) | 3 lines Patch 1353 by Jacob Winther. Add mp4 mapping to mimetypes.py. ........ r58709 | guido.van.rossum | 2007-10-29 15:15:05 -0700 (Mon, 29 Oct 2007) | 6 lines Backport fixes for the code that decodes octal escapes (and for PyString also hex escapes) -- this was reaching beyond the end of the input string buffer, even though it is not supposed to be \0-terminated. This has no visible effect but is clearly the correct thing to do. (In 3.0 it had a visible effect after removing ob_sstate from PyString.) ........ r58710 | kurt.kaiser | 2007-10-29 19:38:54 -0700 (Mon, 29 Oct 2007) | 7 lines check in Tal Einat's update to tabpage.py Patch 1612746 M configDialog.py M NEWS.txt AM tabbedpages.py ........ r58715 | georg.brandl | 2007-10-30 10:51:18 -0700 (Tue, 30 Oct 2007) | 2 lines Use correct markup. ........ r58716 | georg.brandl | 2007-10-30 10:57:12 -0700 (Tue, 30 Oct 2007) | 2 lines Make example about hiding None return values at the prompt clearer. ........ r58728 | neal.norwitz | 2007-10-30 23:33:20 -0700 (Tue, 30 Oct 2007) | 1 line Fix some compiler warnings for signed comparisons on Unix and Windows. ........ r58731 | martin.v.loewis | 2007-10-31 10:19:33 -0700 (Wed, 31 Oct 2007) | 2 lines Adding Christian Heimes. ........ r58737 | raymond.hettinger | 2007-10-31 14:57:58 -0700 (Wed, 31 Oct 2007) | 1 line Clarify the reasons why pickle is almost always better than marshal ........ r58739 | raymond.hettinger | 2007-10-31 15:15:49 -0700 (Wed, 31 Oct 2007) | 1 line Sets are marshalable. ........
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:option:`-O` is used, *all* :term:`bytecode` is optimized; ``.pyc`` files are
ignored and ``.py`` files are compiled to optimized bytecode.
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* Passing two :option:`-O` flags to the Python interpreter (:option:`-OO`) will
cause the bytecode compiler to perform optimizations that could in some rare
cases result in malfunctioning programs. Currently only ``__doc__`` strings are
removed from the bytecode, resulting in more compact :file:`.pyo` files. Since
some programs may rely on having these available, you should only use this
option if you know what you're doing.
* A program doesn't run any faster when it is read from a :file:`.pyc` or
:file:`.pyo` file than when it is read from a :file:`.py` file; the only thing
that's faster about :file:`.pyc` or :file:`.pyo` files is the speed with which
they are loaded.
* When a script is run by giving its name on the command line, the bytecode for
the script is never written to a :file:`.pyc` or :file:`.pyo` file. Thus, the
startup time of a script may be reduced by moving most of its code to a module
and having a small bootstrap script that imports that module. It is also
possible to name a :file:`.pyc` or :file:`.pyo` file directly on the command
line.
* It is possible to have a file called :file:`spam.pyc` (or :file:`spam.pyo`
when :option:`-O` is used) without a file :file:`spam.py` for the same module.
This can be used to distribute a library of Python code in a form that is
moderately hard to reverse engineer.
.. index:: module: compileall
* The module :mod:`compileall` can create :file:`.pyc` files (or :file:`.pyo`
files when :option:`-O` is used) for all modules in a directory.
.. _tut-standardmodules:
Standard Modules
================
.. index:: module: sys
Python comes with a library of standard modules, described in a separate
document, the Python Library Reference ("Library Reference" hereafter). Some
modules are built into the interpreter; these provide access to operations that
are not part of the core of the language but are nevertheless built in, either
for efficiency or to provide access to operating system primitives such as
system calls. The set of such modules is a configuration option which also
depends on the underlying platform For example, the :mod:`winreg` module is only
provided on Windows systems. One particular module deserves some attention:
:mod:`sys`, which is built into every Python interpreter. The variables
``sys.ps1`` and ``sys.ps2`` define the strings used as primary and secondary
prompts::
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>>> import sys
>>> sys.ps1
'>>> '
>>> sys.ps2
'... '
>>> sys.ps1 = 'C> '
C> print('Yuck!')
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Yuck!
C>
These two variables are only defined if the interpreter is in interactive mode.
The variable ``sys.path`` is a list of strings that determines the interpreter's
search path for modules. It is initialized to a default path taken from the
environment variable :envvar:`PYTHONPATH`, or from a built-in default if
:envvar:`PYTHONPATH` is not set. You can modify it using standard list
operations::
>>> import sys
>>> sys.path.append('/ufs/guido/lib/python')
.. _tut-dir:
The :func:`dir` Function
========================
The built-in function :func:`dir` is used to find out which names a module
defines. It returns a sorted list of strings::
>>> import fibo, sys
>>> dir(fibo)
['__name__', 'fib', 'fib2']
>>> dir(sys)
['__displayhook__', '__doc__', '__excepthook__', '__name__', '__stderr__',
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'__stdin__', '__stdout__', '_getframe', 'api_version', 'argv',
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'builtin_module_names', 'byteorder', 'callstats', 'copyright',
'displayhook', 'exc_info', 'excepthook',
'exec_prefix', 'executable', 'exit', 'getdefaultencoding', 'getdlopenflags',
'getrecursionlimit', 'getrefcount', 'hexversion', 'maxint', 'maxunicode',
'meta_path', 'modules', 'path', 'path_hooks', 'path_importer_cache',
'platform', 'prefix', 'ps1', 'ps2', 'setcheckinterval', 'setdlopenflags',
'setprofile', 'setrecursionlimit', 'settrace', 'stderr', 'stdin', 'stdout',
'version', 'version_info', 'warnoptions']
Without arguments, :func:`dir` lists the names you have defined currently::
>>> a = [1, 2, 3, 4, 5]
>>> import fibo
>>> fib = fibo.fib
>>> dir()
['__builtins__', '__doc__', '__file__', '__name__', 'a', 'fib', 'fibo', 'sys']
Note that it lists all types of names: variables, modules, functions, etc.
.. index:: module: builtins
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:func:`dir` does not list the names of built-in functions and variables. If you
want a list of those, they are defined in the standard module
:mod:`builtins`::
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>>> import builtins
>>> dir(builtins)
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['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', 'Buffer
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Error', 'DeprecationWarning', 'EOFError', 'Ellipsis', 'EnvironmentError', 'Excep
tion', 'False', 'FloatingPointError', 'FutureWarning', 'GeneratorExit', 'IOError
', 'ImportError', 'ImportWarning', 'IndentationError', 'IndexError', 'KeyError',
'KeyboardInterrupt', 'LookupError', 'MemoryError', 'NameError', 'None', 'NotImp
lemented', 'NotImplementedError', 'OSError', 'OverflowError', 'PendingDeprecatio
nWarning', 'ReferenceError', 'RuntimeError', 'RuntimeWarning', 'StopIteration',
'SyntaxError', 'SyntaxWarning', 'SystemError', 'SystemExit', 'TabError', 'True',
'TypeError', 'UnboundLocalError', 'UnicodeDecodeError', 'UnicodeEncodeError', '
UnicodeError', 'UnicodeTranslateError', 'UnicodeWarning', 'UserWarning', 'ValueE
rror', 'Warning', 'ZeroDivisionError', '__build_class__', '__debug__', '__doc__'
, '__import__', '__name__', 'abs', 'all', 'any', 'basestring', 'bin', 'bool', 'b
uffer', 'bytes', 'chr', 'chr8', 'classmethod', 'cmp', 'compile', 'complex', 'cop
yright', 'credits', 'delattr', 'dict', 'dir', 'divmod', 'enumerate', 'eval', 'ex
ec', 'exit', 'filter', 'float', 'frozenset', 'getattr', 'globals', 'hasattr', 'h
ash', 'help', 'hex', 'id', 'input', 'int', 'isinstance', 'issubclass', 'iter', '
len', 'license', 'list', 'locals', 'map', 'max', 'memoryview', 'min', 'next', 'o
bject', 'oct', 'open', 'ord', 'pow', 'print', 'property', 'quit', 'range', 'repr
', 'reversed', 'round', 'set', 'setattr', 'slice', 'sorted', 'staticmethod', 'st
r', 'str8', 'sum', 'super', 'trunc', 'tuple', 'type', 'vars', 'zip']
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.. _tut-packages:
Packages
========
Packages are a way of structuring Python's module namespace by using "dotted
module names". For example, the module name :mod:`A.B` designates a submodule
named ``B`` in a package named ``A``. Just like the use of modules saves the
authors of different modules from having to worry about each other's global
variable names, the use of dotted module names saves the authors of multi-module
packages like NumPy or the Python Imaging Library from having to worry about
each other's module names.
Suppose you want to design a collection of modules (a "package") for the uniform
handling of sound files and sound data. There are many different sound file
formats (usually recognized by their extension, for example: :file:`.wav`,
:file:`.aiff`, :file:`.au`), so you may need to create and maintain a growing
collection of modules for the conversion between the various file formats.
There are also many different operations you might want to perform on sound data
(such as mixing, adding echo, applying an equalizer function, creating an
artificial stereo effect), so in addition you will be writing a never-ending
stream of modules to perform these operations. Here's a possible structure for
your package (expressed in terms of a hierarchical filesystem)::
sound/ Top-level package
__init__.py Initialize the sound package
formats/ Subpackage for file format conversions
__init__.py
wavread.py
wavwrite.py
aiffread.py
aiffwrite.py
auread.py
auwrite.py
...
effects/ Subpackage for sound effects
__init__.py
echo.py
surround.py
reverse.py
...
filters/ Subpackage for filters
__init__.py
equalizer.py
vocoder.py
karaoke.py
...
When importing the package, Python searches through the directories on
``sys.path`` looking for the package subdirectory.
The :file:`__init__.py` files are required to make Python treat the directories
as containing packages; this is done to prevent directories with a common name,
such as ``string``, from unintentionally hiding valid modules that occur later
on the module search path. In the simplest case, :file:`__init__.py` can just be
an empty file, but it can also execute initialization code for the package or
set the ``__all__`` variable, described later.
Users of the package can import individual modules from the package, for
example::
import sound.effects.echo
This loads the submodule :mod:`sound.effects.echo`. It must be referenced with
its full name. ::
sound.effects.echo.echofilter(input, output, delay=0.7, atten=4)
An alternative way of importing the submodule is::
from sound.effects import echo
This also loads the submodule :mod:`echo`, and makes it available without its
package prefix, so it can be used as follows::
echo.echofilter(input, output, delay=0.7, atten=4)
Yet another variation is to import the desired function or variable directly::
from sound.effects.echo import echofilter
Again, this loads the submodule :mod:`echo`, but this makes its function
:func:`echofilter` directly available::
echofilter(input, output, delay=0.7, atten=4)
Note that when using ``from package import item``, the item can be either a
submodule (or subpackage) of the package, or some other name defined in the
package, like a function, class or variable. The ``import`` statement first
tests whether the item is defined in the package; if not, it assumes it is a
module and attempts to load it. If it fails to find it, an :exc:`ImportError`
exception is raised.
Contrarily, when using syntax like ``import item.subitem.subsubitem``, each item
except for the last must be a package; the last item can be a module or a
package but can't be a class or function or variable defined in the previous
item.
.. _tut-pkg-import-star:
Importing \* From a Package
---------------------------
.. index:: single: __all__
Now what happens when the user writes ``from sound.effects import *``? Ideally,
one would hope that this somehow goes out to the filesystem, finds which
submodules are present in the package, and imports them all. Unfortunately,
this operation does not work very well on Windows platforms, where the
filesystem does not always have accurate information about the case of a
filename! On these platforms, there is no guaranteed way to know whether a file
:file:`ECHO.PY` should be imported as a module :mod:`echo`, :mod:`Echo` or
:mod:`ECHO`. (For example, Windows 95 has the annoying practice of showing all
file names with a capitalized first letter.) The DOS 8+3 filename restriction
adds another interesting problem for long module names.
The only solution is for the package author to provide an explicit index of the
package. The import statement uses the following convention: if a package's
:file:`__init__.py` code defines a list named ``__all__``, it is taken to be the
list of module names that should be imported when ``from package import *`` is
encountered. It is up to the package author to keep this list up-to-date when a
new version of the package is released. Package authors may also decide not to
support it, if they don't see a use for importing \* from their package. For
example, the file :file:`sounds/effects/__init__.py` could contain the following
code::
__all__ = ["echo", "surround", "reverse"]
This would mean that ``from sound.effects import *`` would import the three
named submodules of the :mod:`sound` package.
If ``__all__`` is not defined, the statement ``from sound.effects import *``
does *not* import all submodules from the package :mod:`sound.effects` into the
current namespace; it only ensures that the package :mod:`sound.effects` has
been imported (possibly running any initialization code in :file:`__init__.py`)
and then imports whatever names are defined in the package. This includes any
names defined (and submodules explicitly loaded) by :file:`__init__.py`. It
also includes any submodules of the package that were explicitly loaded by
previous import statements. Consider this code::
import sound.effects.echo
import sound.effects.surround
from sound.effects import *
In this example, the echo and surround modules are imported in the current
namespace because they are defined in the :mod:`sound.effects` package when the
``from...import`` statement is executed. (This also works when ``__all__`` is
defined.)
Note that in general the practice of importing ``*`` from a module or package is
frowned upon, since it often causes poorly readable code. However, it is okay to
use it to save typing in interactive sessions, and certain modules are designed
to export only names that follow certain patterns.
Remember, there is nothing wrong with using ``from Package import
specific_submodule``! In fact, this is the recommended notation unless the
importing module needs to use submodules with the same name from different
packages.
Intra-package References
------------------------
When packages are structured into subpackages (as with the :mod:`sound` package
in the example), you can use absolute imports to refer to submodules of siblings
packages. For example, if the module :mod:`sound.filters.vocoder` needs to use
the :mod:`echo` module in the :mod:`sound.effects` package, it can use ``from
sound.effects import echo``.
You can also write relative imports, with the ``from module import name`` form
of import statement. These imports use leading dots to indicate the current and
parent packages involved in the relative import. From the :mod:`surround`
module for example, you might use::
2007-08-15 11:28:22 -03:00
from . import echo
from .. import formats
from ..filters import equalizer
Note that relative imports are based on the name of the current module. Since
the name of the main module is always ``"__main__"``, modules intended for use
as the main module of a Python application must always use absolute imports.
2007-08-15 11:28:22 -03:00
Packages in Multiple Directories
--------------------------------
Packages support one more special attribute, :attr:`__path__`. This is
initialized to be a list containing the name of the directory holding the
package's :file:`__init__.py` before the code in that file is executed. This
variable can be modified; doing so affects future searches for modules and
subpackages contained in the package.
While this feature is not often needed, it can be used to extend the set of
modules found in a package.
.. rubric:: Footnotes
.. [#] In fact function definitions are also 'statements' that are 'executed'; the
execution enters the function name in the module's global symbol table.