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# SOME DESCRIPTIVE TITLE.
# Copyright (C) 2001 Python Software Foundation
# This file is distributed under the same license as the Python package.
# FIRST AUTHOR <EMAIL@ADDRESS>, YEAR.
#
# Translators:
# python-doc bot, 2025
#
#, fuzzy
msgid ""
msgstr ""
"Project-Id-Version: Python 3.14\n"
"Report-Msgid-Bugs-To: \n"
"POT-Creation-Date: 2026-04-11 14:31+0000\n"
"PO-Revision-Date: 2025-09-16 00:02+0000\n"
"Last-Translator: python-doc bot, 2025\n"
"Language-Team: Polish (https://app.transifex.com/python-doc/teams/5390/pl/)\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
"Language: pl\n"
"Plural-Forms: nplurals=4; plural=(n==1 ? 0 : (n%10>=2 && n%10<=4) && "
"(n%100<12 || n%100>14) ? 1 : n!=1 && (n%10>=0 && n%10<=1) || (n%10>=5 && "
"n%10<=9) || (n%100>=12 && n%100<=14) ? 2 : 3);\n"
msgid "What's New in Python 2.5"
msgstr ""
msgid "Author"
msgstr "Autor"
msgid "A.M. Kuchling"
msgstr ""
msgid ""
"This article explains the new features in Python 2.5. The final release of "
"Python 2.5 is scheduled for August 2006; :pep:`356` describes the planned "
"release schedule. Python 2.5 was released on September 19, 2006."
msgstr ""
msgid ""
"The changes in Python 2.5 are an interesting mix of language and library "
"improvements. The library enhancements will be more important to Python's "
"user community, I think, because several widely useful packages were added. "
"New modules include ElementTree for XML processing (:mod:`xml.etree`), the "
"SQLite database module (:mod:`sqlite`), and the :mod:`ctypes` module for "
"calling C functions."
msgstr ""
msgid ""
"The language changes are of middling significance. Some pleasant new "
"features were added, but most of them aren't features that you'll use every "
"day. Conditional expressions were finally added to the language using a "
"novel syntax; see section :ref:`pep-308`. The new ':keyword:`with`' "
"statement will make writing cleanup code easier (section :ref:`pep-343`). "
"Values can now be passed into generators (section :ref:`pep-342`). Imports "
"are now visible as either absolute or relative (section :ref:`pep-328`). "
"Some corner cases of exception handling are handled better (section :ref:"
"`pep-341`). All these improvements are worthwhile, but they're improvements "
"to one specific language feature or another; none of them are broad "
"modifications to Python's semantics."
msgstr ""
msgid ""
"As well as the language and library additions, other improvements and "
"bugfixes were made throughout the source tree. A search through the SVN "
"change logs finds there were 353 patches applied and 458 bugs fixed between "
"Python 2.4 and 2.5. (Both figures are likely to be underestimates.)"
msgstr ""
msgid ""
"This article doesn't try to be a complete specification of the new features; "
"instead changes are briefly introduced using helpful examples. For full "
"details, you should always refer to the documentation for Python 2.5 at "
"https://docs.python.org. If you want to understand the complete "
"implementation and design rationale, refer to the PEP for a particular new "
"feature."
msgstr ""
msgid ""
"Comments, suggestions, and error reports for this document are welcome; "
"please e-mail them to the author or open a bug in the Python bug tracker."
msgstr ""
msgid "PEP 308: Conditional Expressions"
msgstr ""
msgid ""
"For a long time, people have been requesting a way to write conditional "
"expressions, which are expressions that return value A or value B depending "
"on whether a Boolean value is true or false. A conditional expression lets "
"you write a single assignment statement that has the same effect as the "
"following::"
msgstr ""
msgid ""
"if condition:\n"
" x = true_value\n"
"else:\n"
" x = false_value"
msgstr ""
msgid ""
"There have been endless tedious discussions of syntax on both python-dev and "
"comp.lang.python. A vote was even held that found the majority of voters "
"wanted conditional expressions in some form, but there was no syntax that "
"was preferred by a clear majority. Candidates included C's ``cond ? true_v : "
"false_v``, ``if cond then true_v else false_v``, and 16 other variations."
msgstr ""
msgid "Guido van Rossum eventually chose a surprising syntax::"
msgstr ""
msgid "x = true_value if condition else false_value"
msgstr ""
msgid ""
"Evaluation is still lazy as in existing Boolean expressions, so the order of "
"evaluation jumps around a bit. The *condition* expression in the middle is "
"evaluated first, and the *true_value* expression is evaluated only if the "
"condition was true. Similarly, the *false_value* expression is only "
"evaluated when the condition is false."
msgstr ""
msgid ""
"This syntax may seem strange and backwards; why does the condition go in the "
"*middle* of the expression, and not in the front as in C's ``c ? x : y``? "
"The decision was checked by applying the new syntax to the modules in the "
"standard library and seeing how the resulting code read. In many cases "
"where a conditional expression is used, one value seems to be the 'common "
"case' and one value is an 'exceptional case', used only on rarer occasions "
"when the condition isn't met. The conditional syntax makes this pattern a "
"bit more obvious::"
msgstr ""
msgid "contents = ((doc + '\\n') if doc else '')"
msgstr ""
msgid ""
"I read the above statement as meaning \"here *contents* is usually assigned "
"a value of ``doc+'\\n'``; sometimes *doc* is empty, in which special case "
"an empty string is returned.\" I doubt I will use conditional expressions "
"very often where there isn't a clear common and uncommon case."
msgstr ""
msgid ""
"There was some discussion of whether the language should require surrounding "
"conditional expressions with parentheses. The decision was made to *not* "
"require parentheses in the Python language's grammar, but as a matter of "
"style I think you should always use them. Consider these two statements::"
msgstr ""
msgid ""
"# First version -- no parens\n"
"level = 1 if logging else 0\n"
"\n"
"# Second version -- with parens\n"
"level = (1 if logging else 0)"
msgstr ""
msgid ""
"In the first version, I think a reader's eye might group the statement into "
"'level = 1', 'if logging', 'else 0', and think that the condition decides "
"whether the assignment to *level* is performed. The second version reads "
"better, in my opinion, because it makes it clear that the assignment is "
"always performed and the choice is being made between two values."
msgstr ""
msgid ""
"Another reason for including the brackets: a few odd combinations of list "
"comprehensions and lambdas could look like incorrect conditional "
"expressions. See :pep:`308` for some examples. If you put parentheses "
"around your conditional expressions, you won't run into this case."
msgstr ""
msgid ":pep:`308` - Conditional Expressions"
msgstr ""
msgid ""
"PEP written by Guido van Rossum and Raymond D. Hettinger; implemented by "
"Thomas Wouters."
msgstr ""
msgid "PEP 309: Partial Function Application"
msgstr ""
msgid ""
"The :mod:`functools` module is intended to contain tools for functional-"
"style programming."
msgstr ""
msgid ""
"One useful tool in this module is the :func:`partial` function. For programs "
"written in a functional style, you'll sometimes want to construct variants "
"of existing functions that have some of the parameters filled in. Consider "
"a Python function ``f(a, b, c)``; you could create a new function ``g(b, "
"c)`` that was equivalent to ``f(1, b, c)``. This is called \"partial "
"function application\"."
msgstr ""
msgid ""
":func:`partial` takes the arguments ``(function, arg1, arg2, ... "
"kwarg1=value1, kwarg2=value2)``. The resulting object is callable, so you "
"can just call it to invoke *function* with the filled-in arguments."
msgstr ""
msgid "Here's a small but realistic example::"
msgstr ""
msgid ""
"import functools\n"
"\n"
"def log (message, subsystem):\n"
" \"Write the contents of 'message' to the specified subsystem.\"\n"
" print '%s: %s' % (subsystem, message)\n"
" ...\n"
"\n"
"server_log = functools.partial(log, subsystem='server')\n"
"server_log('Unable to open socket')"
msgstr ""
msgid ""
"Here's another example, from a program that uses PyGTK. Here a context-"
"sensitive pop-up menu is being constructed dynamically. The callback "
"provided for the menu option is a partially applied version of the :meth:"
"`open_item` method, where the first argument has been provided. ::"
msgstr ""
msgid ""
"...\n"
"class Application:\n"
" def open_item(self, path):\n"
" ...\n"
" def init (self):\n"
" open_func = functools.partial(self.open_item, item_path)\n"
" popup_menu.append( (\"Open\", open_func, 1) )"
msgstr ""
msgid ""
"Another function in the :mod:`functools` module is the "
"``update_wrapper(wrapper, wrapped)`` function that helps you write well-"
"behaved decorators. :func:`update_wrapper` copies the name, module, and "
"docstring attribute to a wrapper function so that tracebacks inside the "
"wrapped function are easier to understand. For example, you might write::"
msgstr ""
msgid ""
"def my_decorator(f):\n"
" def wrapper(*args, **kwds):\n"
" print 'Calling decorated function'\n"
" return f(*args, **kwds)\n"
" functools.update_wrapper(wrapper, f)\n"
" return wrapper"
msgstr ""
msgid ""
":func:`wraps` is a decorator that can be used inside your own decorators to "
"copy the wrapped function's information. An alternate version of the "
"previous example would be::"
msgstr ""
msgid ""
"def my_decorator(f):\n"
" @functools.wraps(f)\n"
" def wrapper(*args, **kwds):\n"
" print 'Calling decorated function'\n"
" return f(*args, **kwds)\n"
" return wrapper"
msgstr ""
msgid ":pep:`309` - Partial Function Application"
msgstr ""
msgid ""
"PEP proposed and written by Peter Harris; implemented by Hye-Shik Chang and "
"Nick Coghlan, with adaptations by Raymond Hettinger."
msgstr ""
msgid "PEP 314: Metadata for Python Software Packages v1.1"
msgstr ""
msgid ""
"Some simple dependency support was added to Distutils. The :func:`setup` "
"function now has ``requires``, ``provides``, and ``obsoletes`` keyword "
"parameters. When you build a source distribution using the ``sdist`` "
"command, the dependency information will be recorded in the :file:`PKG-INFO` "
"file."
msgstr ""
msgid ""
"Another new keyword parameter is ``download_url``, which should be set to a "
"URL for the package's source code. This means it's now possible to look up "
"an entry in the package index, determine the dependencies for a package, and "
"download the required packages. ::"
msgstr ""
msgid ""
"VERSION = '1.0'\n"
"setup(name='PyPackage',\n"
" version=VERSION,\n"
" requires=['numarray', 'zlib (>=1.1.4)'],\n"
" obsoletes=['OldPackage']\n"
" download_url=('http://www.example.com/pypackage/dist/pkg-%s.tar.gz'\n"
" % VERSION),\n"
" )"
msgstr ""
msgid ""
"Another new enhancement to the Python package index at https://pypi.org is "
"storing source and binary archives for a package. The new :command:`upload` "
"Distutils command will upload a package to the repository."
msgstr ""
msgid ""
"Before a package can be uploaded, you must be able to build a distribution "
"using the :command:`sdist` Distutils command. Once that works, you can run "
"``python setup.py upload`` to add your package to the PyPI archive. "
"Optionally you can GPG-sign the package by supplying the :option:`!--sign` "
"and :option:`!--identity` options."
msgstr ""
msgid ""
"Package uploading was implemented by Martin von Löwis and Richard Jones."
msgstr ""
msgid ":pep:`314` - Metadata for Python Software Packages v1.1"
msgstr ""
msgid ""
"PEP proposed and written by A.M. Kuchling, Richard Jones, and Fred Drake; "
"implemented by Richard Jones and Fred Drake."
msgstr ""
msgid "PEP 328: Absolute and Relative Imports"
msgstr ""
msgid ""
"The simpler part of :pep:`328` was implemented in Python 2.4: parentheses "
"could now be used to enclose the names imported from a module using the "
"``from ... import ...`` statement, making it easier to import many different "
"names."
msgstr ""
msgid ""
"The more complicated part has been implemented in Python 2.5: importing a "
"module can be specified to use absolute or package-relative imports. The "
"plan is to move toward making absolute imports the default in future "
"versions of Python."
msgstr ""
msgid "Let's say you have a package directory like this::"
msgstr ""
msgid ""
"pkg/\n"
"pkg/__init__.py\n"
"pkg/main.py\n"
"pkg/string.py"
msgstr ""
msgid ""
"This defines a package named :mod:`pkg` containing the :mod:`pkg.main` and :"
"mod:`pkg.string` submodules."
msgstr ""
msgid ""
"Consider the code in the :file:`main.py` module. What happens if it "
"executes the statement ``import string``? In Python 2.4 and earlier, it "
"will first look in the package's directory to perform a relative import, "
"finds :file:`pkg/string.py`, imports the contents of that file as the :mod:"
"`pkg.string` module, and that module is bound to the name ``string`` in the :"
"mod:`pkg.main` module's namespace."
msgstr ""
msgid ""
"That's fine if :mod:`pkg.string` was what you wanted. But what if you "
"wanted Python's standard :mod:`string` module? There's no clean way to "
"ignore :mod:`pkg.string` and look for the standard module; generally you had "
"to look at the contents of ``sys.modules``, which is slightly unclean. "
"Holger Krekel's :mod:`py.std` package provides a tidier way to perform "
"imports from the standard library, ``import py; py.std.string.join()``, but "
"that package isn't available on all Python installations."
msgstr ""
msgid ""
"Reading code which relies on relative imports is also less clear, because a "
"reader may be confused about which module, :mod:`string` or :mod:`pkg."
"string`, is intended to be used. Python users soon learned not to duplicate "
"the names of standard library modules in the names of their packages' "
"submodules, but you can't protect against having your submodule's name being "
"used for a new module added in a future version of Python."
msgstr ""
msgid ""
"In Python 2.5, you can switch :keyword:`import`'s behaviour to absolute "
"imports using a ``from __future__ import absolute_import`` directive. This "
"absolute-import behaviour will become the default in a future version "
"(probably Python 2.7). Once absolute imports are the default, ``import "
"string`` will always find the standard library's version. It's suggested "
"that users should begin using absolute imports as much as possible, so it's "
"preferable to begin writing ``from pkg import string`` in your code."
msgstr ""
msgid ""
"Relative imports are still possible by adding a leading period to the "
"module name when using the ``from ... import`` form::"
msgstr ""
msgid ""
"# Import names from pkg.string\n"
"from .string import name1, name2\n"
"# Import pkg.string\n"
"from . import string"
msgstr ""
msgid ""
"This imports the :mod:`string` module relative to the current package, so "
"in :mod:`pkg.main` this will import *name1* and *name2* from :mod:`pkg."
"string`. Additional leading periods perform the relative import starting "
"from the parent of the current package. For example, code in the :mod:`A.B."
"C` module can do::"
msgstr ""
msgid ""
"from . import D # Imports A.B.D\n"
"from .. import E # Imports A.E\n"
"from ..F import G # Imports A.F.G"
msgstr ""
msgid ""
"Leading periods cannot be used with the ``import modname`` form of the "
"import statement, only the ``from ... import`` form."
msgstr ""
msgid ":pep:`328` - Imports: Multi-Line and Absolute/Relative"
msgstr ""
msgid "PEP written by Aahz; implemented by Thomas Wouters."
msgstr ""
msgid "https://pylib.readthedocs.io/"
msgstr "https://pylib.readthedocs.io/"
msgid ""
"The py library by Holger Krekel, which contains the :mod:`py.std` package."
msgstr ""
msgid "PEP 338: Executing Modules as Scripts"
msgstr ""
msgid ""
"The :option:`-m` switch added in Python 2.4 to execute a module as a script "
"gained a few more abilities. Instead of being implemented in C code inside "
"the Python interpreter, the switch now uses an implementation in a new "
"module, :mod:`runpy`."
msgstr ""
msgid ""
"The :mod:`runpy` module implements a more sophisticated import mechanism so "
"that it's now possible to run modules in a package such as :mod:`pychecker."
"checker`. The module also supports alternative import mechanisms such as "
"the :mod:`zipimport` module. This means you can add a .zip archive's path "
"to ``sys.path`` and then use the :option:`-m` switch to execute code from "
"the archive."
msgstr ""
msgid ":pep:`338` - Executing modules as scripts"
msgstr ""
msgid "PEP written and implemented by Nick Coghlan."
msgstr ""
msgid "PEP 341: Unified try/except/finally"
msgstr ""
msgid ""
"Until Python 2.5, the :keyword:`try` statement came in two flavours. You "
"could use a :keyword:`finally` block to ensure that code is always executed, "
"or one or more :keyword:`except` blocks to catch specific exceptions. You "
"couldn't combine both :keyword:`!except` blocks and a :keyword:`!finally` "
"block, because generating the right bytecode for the combined version was "
"complicated and it wasn't clear what the semantics of the combined statement "
"should be."
msgstr ""
msgid ""
"Guido van Rossum spent some time working with Java, which does support the "
"equivalent of combining :keyword:`except` blocks and a :keyword:`finally` "
"block, and this clarified what the statement should mean. In Python 2.5, "
"you can now write::"
msgstr ""
msgid ""
"try:\n"
" block-1 ...\n"
"except Exception1:\n"
" handler-1 ...\n"
"except Exception2:\n"
" handler-2 ...\n"
"else:\n"
" else-block\n"
"finally:\n"
" final-block"
msgstr ""
msgid ""
"The code in *block-1* is executed. If the code raises an exception, the "
"various :keyword:`except` blocks are tested: if the exception is of class :"
"class:`Exception1`, *handler-1* is executed; otherwise if it's of class :"
"class:`Exception2`, *handler-2* is executed, and so forth. If no exception "
"is raised, the *else-block* is executed."
msgstr ""
msgid ""
"No matter what happened previously, the *final-block* is executed once the "
"code block is complete and any raised exceptions handled. Even if there's an "
"error in an exception handler or the *else-block* and a new exception is "
"raised, the code in the *final-block* is still run."
msgstr ""
msgid ":pep:`341` - Unifying try-except and try-finally"
msgstr ""
msgid "PEP written by Georg Brandl; implementation by Thomas Lee."
msgstr ""
msgid "PEP 342: New Generator Features"
msgstr ""
msgid ""
"Python 2.5 adds a simple way to pass values *into* a generator. As "
"introduced in Python 2.3, generators only produce output; once a generator's "
"code was invoked to create an iterator, there was no way to pass any new "
"information into the function when its execution is resumed. Sometimes the "
"ability to pass in some information would be useful. Hackish solutions to "
"this include making the generator's code look at a global variable and then "
"changing the global variable's value, or passing in some mutable object that "
"callers then modify."
msgstr ""
msgid "To refresh your memory of basic generators, here's a simple example::"
msgstr ""
msgid ""
"def counter (maximum):\n"
" i = 0\n"
" while i < maximum:\n"
" yield i\n"
" i += 1"
msgstr ""
msgid ""
"When you call ``counter(10)``, the result is an iterator that returns the "
"values from 0 up to 9. On encountering the :keyword:`yield` statement, the "
"iterator returns the provided value and suspends the function's execution, "
"preserving the local variables. Execution resumes on the following call to "
"the iterator's :meth:`next` method, picking up after the :keyword:`!yield` "
"statement."
msgstr ""
msgid ""
"In Python 2.3, :keyword:`yield` was a statement; it didn't return any "
"value. In 2.5, :keyword:`!yield` is now an expression, returning a value "
"that can be assigned to a variable or otherwise operated on::"
msgstr ""
msgid "val = (yield i)"
msgstr ""
msgid ""
"I recommend that you always put parentheses around a :keyword:`yield` "
"expression when you're doing something with the returned value, as in the "
"above example. The parentheses aren't always necessary, but it's easier to "
"always add them instead of having to remember when they're needed."
msgstr ""
msgid ""
"(:pep:`342` explains the exact rules, which are that a :keyword:`yield`\\ -"
"expression must always be parenthesized except when it occurs at the top-"
"level expression on the right-hand side of an assignment. This means you "
"can write ``val = yield i`` but have to use parentheses when there's an "
"operation, as in ``val = (yield i) + 12``.)"
msgstr ""
msgid ""
"Values are sent into a generator by calling its ``send(value)`` method. The "
"generator's code is then resumed and the :keyword:`yield` expression returns "
"the specified *value*. If the regular :meth:`next` method is called, the :"
"keyword:`!yield` returns :const:`None`."
msgstr ""
msgid ""
"Here's the previous example, modified to allow changing the value of the "
"internal counter. ::"
msgstr ""
msgid ""
"def counter (maximum):\n"
" i = 0\n"
" while i < maximum:\n"
" val = (yield i)\n"
" # If value provided, change counter\n"
" if val is not None:\n"
" i = val\n"
" else:\n"
" i += 1"
msgstr ""
msgid "And here's an example of changing the counter::"
msgstr ""
msgid ""
">>> it = counter(10)\n"
">>> print it.next()\n"
"0\n"
">>> print it.next()\n"
"1\n"
">>> print it.send(8)\n"
"8\n"
">>> print it.next()\n"
"9\n"
">>> print it.next()\n"
"Traceback (most recent call last):\n"
" File \"t.py\", line 15, in ?\n"
" print it.next()\n"
"StopIteration"
msgstr ""
msgid ""
":keyword:`yield` will usually return :const:`None`, so you should always "
"check for this case. Don't just use its value in expressions unless you're "
"sure that the :meth:`send` method will be the only method used to resume "
"your generator function."
msgstr ""
msgid ""
"In addition to :meth:`send`, there are two other new methods on generators:"
msgstr ""
msgid ""
"``throw(type, value=None, traceback=None)`` is used to raise an exception "
"inside the generator; the exception is raised by the :keyword:`yield` "
"expression where the generator's execution is paused."
msgstr ""
msgid ""
":meth:`close` raises a new :exc:`GeneratorExit` exception inside the "
"generator to terminate the iteration. On receiving this exception, the "
"generator's code must either raise :exc:`GeneratorExit` or :exc:"
"`StopIteration`. Catching the :exc:`GeneratorExit` exception and returning "
"a value is illegal and will trigger a :exc:`RuntimeError`; if the function "
"raises some other exception, that exception is propagated to the caller. :"
"meth:`close` will also be called by Python's garbage collector when the "
"generator is garbage-collected."
msgstr ""
msgid ""
"If you need to run cleanup code when a :exc:`GeneratorExit` occurs, I "
"suggest using a ``try: ... finally:`` suite instead of catching :exc:"
"`GeneratorExit`."
msgstr ""
msgid ""
"The cumulative effect of these changes is to turn generators from one-way "
"producers of information into both producers and consumers."
msgstr ""
msgid ""
"Generators also become *coroutines*, a more generalized form of subroutines. "
"Subroutines are entered at one point and exited at another point (the top of "
"the function, and a :keyword:`return` statement), but coroutines can be "
"entered, exited, and resumed at many different points (the :keyword:`yield` "
"statements). We'll have to figure out patterns for using coroutines "
"effectively in Python."
msgstr ""
msgid ""
"The addition of the :meth:`close` method has one side effect that isn't "
"obvious. :meth:`close` is called when a generator is garbage-collected, so "
"this means the generator's code gets one last chance to run before the "
"generator is destroyed. This last chance means that ``try...finally`` "
"statements in generators can now be guaranteed to work; the :keyword:"
"`finally` clause will now always get a chance to run. The syntactic "
"restriction that you couldn't mix :keyword:`yield` statements with a ``try..."
"finally`` suite has therefore been removed. This seems like a minor bit of "
"language trivia, but using generators and ``try...finally`` is actually "
"necessary in order to implement the :keyword:`with` statement described by :"
"pep:`343`. I'll look at this new statement in the following section."
msgstr ""
msgid ""
"Another even more esoteric effect of this change: previously, the :attr:"
"`gi_frame` attribute of a generator was always a frame object. It's now "
"possible for :attr:`gi_frame` to be ``None`` once the generator has been "
"exhausted."
msgstr ""
msgid ":pep:`342` - Coroutines via Enhanced Generators"
msgstr ""
msgid ""
"PEP written by Guido van Rossum and Phillip J. Eby; implemented by Phillip "
"J. Eby. Includes examples of some fancier uses of generators as coroutines."
msgstr ""
msgid ""
"Earlier versions of these features were proposed in :pep:`288` by Raymond "
"Hettinger and :pep:`325` by Samuele Pedroni."
msgstr ""
msgid "https://en.wikipedia.org/wiki/Coroutine"
msgstr "https://en.wikipedia.org/wiki/Coroutine"
msgid "The Wikipedia entry for coroutines."
msgstr ""
msgid ""
"https://web.archive.org/web/20160321211320/http://www.sidhe.org/~dan/blog/"
"archives/000178.html"
msgstr ""
"https://web.archive.org/web/20160321211320/http://www.sidhe.org/~dan/blog/"
"archives/000178.html"
msgid ""
"An explanation of coroutines from a Perl point of view, written by Dan "
"Sugalski."
msgstr ""
msgid "PEP 343: The 'with' statement"
msgstr ""
msgid ""
"The ':keyword:`with`' statement clarifies code that previously would use "
"``try...finally`` blocks to ensure that clean-up code is executed. In this "
"section, I'll discuss the statement as it will commonly be used. In the "
"next section, I'll examine the implementation details and show how to write "
"objects for use with this statement."
msgstr ""
msgid ""
"The ':keyword:`with`' statement is a new control-flow structure whose basic "
"structure is::"
msgstr ""
msgid ""
"with expression [as variable]:\n"
" with-block"
msgstr ""
msgid ""
"The expression is evaluated, and it should result in an object that supports "
"the context management protocol (that is, has :meth:`~object.__enter__` and :"
"meth:`~object.__exit__` methods."
msgstr ""
msgid ""
"The object's :meth:`~object.__enter__` is called before *with-block* is "
"executed and therefore can run set-up code. It also may return a value that "
"is bound to the name *variable*, if given. (Note carefully that *variable* "
"is *not* assigned the result of *expression*.)"
msgstr ""
msgid ""
"After execution of the *with-block* is finished, the object's :meth:`~object."
"__exit__` method is called, even if the block raised an exception, and can "
"therefore run clean-up code."
msgstr ""
msgid ""
"To enable the statement in Python 2.5, you need to add the following "
"directive to your module::"
msgstr ""
msgid "from __future__ import with_statement"
msgstr ""
msgid "The statement will always be enabled in Python 2.6."
msgstr ""
msgid ""
"Some standard Python objects now support the context management protocol and "
"can be used with the ':keyword:`with`' statement. File objects are one "
"example::"
msgstr ""
msgid ""
"with open('/etc/passwd', 'r') as f:\n"
" for line in f:\n"
" print line\n"
" ... more processing code ..."
msgstr ""
msgid ""
"After this statement has executed, the file object in *f* will have been "
"automatically closed, even if the :keyword:`for` loop raised an exception "
"part-way through the block."
msgstr ""
msgid ""
"In this case, *f* is the same object created by :func:`open`, because :meth:"
"`~object.__enter__` returns *self*."
msgstr ""
msgid ""
"The :mod:`threading` module's locks and condition variables also support "
"the ':keyword:`with`' statement::"
msgstr ""
msgid ""
"lock = threading.Lock()\n"
"with lock:\n"
" # Critical section of code\n"
" ..."
msgstr ""
msgid ""
"The lock is acquired before the block is executed and always released once "
"the block is complete."
msgstr ""
msgid ""
"The new :func:`localcontext` function in the :mod:`decimal` module makes it "
"easy to save and restore the current decimal context, which encapsulates the "
"desired precision and rounding characteristics for computations::"
msgstr ""
msgid ""
"from decimal import Decimal, Context, localcontext\n"
"\n"
"# Displays with default precision of 28 digits\n"
"v = Decimal('578')\n"
"print v.sqrt()\n"
"\n"
"with localcontext(Context(prec=16)):\n"
" # All code in this block uses a precision of 16 digits.\n"
" # The original context is restored on exiting the block.\n"
" print v.sqrt()"
msgstr ""
msgid "Writing Context Managers"
msgstr ""
msgid ""
"Under the hood, the ':keyword:`with`' statement is fairly complicated. Most "
"people will only use ':keyword:`!with`' in company with existing objects and "
"don't need to know these details, so you can skip the rest of this section "
"if you like. Authors of new objects will need to understand the details of "
"the underlying implementation and should keep reading."
msgstr ""
msgid "A high-level explanation of the context management protocol is:"
msgstr ""
msgid ""
"The expression is evaluated and should result in an object called a "
"\"context manager\". The context manager must have :meth:`~object."
"__enter__` and :meth:`~object.__exit__` methods."
msgstr ""
msgid ""
"The context manager's :meth:`~object.__enter__` method is called. The value "
"returned is assigned to *VAR*. If no ``'as VAR'`` clause is present, the "
"value is simply discarded."
msgstr ""
msgid "The code in *BLOCK* is executed."
msgstr ""
msgid ""
"If *BLOCK* raises an exception, the ``__exit__(type, value, traceback)`` is "
"called with the exception details, the same values returned by :func:`sys."
"exc_info`. The method's return value controls whether the exception is re-"
"raised: any false value re-raises the exception, and ``True`` will result in "
"suppressing it. You'll only rarely want to suppress the exception, because "
"if you do the author of the code containing the ':keyword:`with`' statement "
"will never realize anything went wrong."
msgstr ""
msgid ""
"If *BLOCK* didn't raise an exception, the :meth:`~object.__exit__` method "
"is still called, but *type*, *value*, and *traceback* are all ``None``."
msgstr ""
msgid ""
"Let's think through an example. I won't present detailed code but will only "
"sketch the methods necessary for a database that supports transactions."
msgstr ""
msgid ""
"(For people unfamiliar with database terminology: a set of changes to the "
"database are grouped into a transaction. Transactions can be either "
"committed, meaning that all the changes are written into the database, or "
"rolled back, meaning that the changes are all discarded and the database is "
"unchanged. See any database textbook for more information.)"
msgstr ""
msgid ""
"Let's assume there's an object representing a database connection. Our goal "
"will be to let the user write code like this::"
msgstr ""
msgid ""
"db_connection = DatabaseConnection()\n"
"with db_connection as cursor:\n"
" cursor.execute('insert into ...')\n"
" cursor.execute('delete from ...')\n"
" # ... more operations ..."
msgstr ""
msgid ""
"The transaction should be committed if the code in the block runs flawlessly "
"or rolled back if there's an exception. Here's the basic interface for :"
"class:`DatabaseConnection` that I'll assume::"
msgstr ""
msgid ""
"class DatabaseConnection:\n"
" # Database interface\n"
" def cursor (self):\n"
" \"Returns a cursor object and starts a new transaction\"\n"
" def commit (self):\n"
" \"Commits current transaction\"\n"
" def rollback (self):\n"
" \"Rolls back current transaction\""
msgstr ""
msgid ""
"The :meth:`~object.__enter__` method is pretty easy, having only to start a "
"new transaction. For this application the resulting cursor object would be "
"a useful result, so the method will return it. The user can then add ``as "
"cursor`` to their ':keyword:`with`' statement to bind the cursor to a "
"variable name. ::"
msgstr ""
msgid ""
"class DatabaseConnection:\n"
" ...\n"
" def __enter__ (self):\n"
" # Code to start a new transaction\n"
" cursor = self.cursor()\n"
" return cursor"
msgstr ""
msgid ""
"The :meth:`~object.__exit__` method is the most complicated because it's "
"where most of the work has to be done. The method has to check if an "
"exception occurred. If there was no exception, the transaction is "
"committed. The transaction is rolled back if there was an exception."
msgstr ""
msgid ""
"In the code below, execution will just fall off the end of the function, "
"returning the default value of ``None``. ``None`` is false, so the "
"exception will be re-raised automatically. If you wished, you could be more "
"explicit and add a :keyword:`return` statement at the marked location. ::"
msgstr ""
msgid ""
"class DatabaseConnection:\n"
" ...\n"
" def __exit__ (self, type, value, tb):\n"
" if tb is None:\n"
" # No exception, so commit\n"
" self.commit()\n"
" else:\n"
" # Exception occurred, so rollback.\n"
" self.rollback()\n"
" # return False"
msgstr ""
msgid "The contextlib module"
msgstr ""
msgid ""
"The new :mod:`contextlib` module provides some functions and a decorator "
"that are useful for writing objects for use with the ':keyword:`with`' "
"statement."
msgstr ""
msgid ""
"The decorator is called :func:`contextmanager`, and lets you write a single "
"generator function instead of defining a new class. The generator should "
"yield exactly one value. The code up to the :keyword:`yield` will be "
"executed as the :meth:`~object.__enter__` method, and the value yielded will "
"be the method's return value that will get bound to the variable in the ':"
"keyword:`with`' statement's :keyword:`!as` clause, if any. The code after "
"the :keyword:`yield` will be executed in the :meth:`~object.__exit__` "
"method. Any exception raised in the block will be raised by the :keyword:`!"
"yield` statement."
msgstr ""
msgid ""
"Our database example from the previous section could be written using this "
"decorator as::"
msgstr ""
msgid ""
"from contextlib import contextmanager\n"
"\n"
"@contextmanager\n"