The arguments to a generator function which is declared as a
contextmanager are stored inside the context manager, and
thus are kept alive, even when it is used as a regular context
manager, and not as a function decorator (where it needs
the original arguments to recreate the generator on each
call).

This is a possible unnecessary memory leak, so this changes
contextmanager.__enter__ to release the saved arguments,
as that method being called means that particular CM instance
isn't going to need to recreate the underlying generator.

Patch by Martin Teichmann.

Adds a simpler and faster alternative to ExitStack for handling
single optional context managers without having to change the
lexical structure of your code.

* Remove Setup.config
* Always define WITH_THREAD for compatibility.

contextlib.AbstractContextManager now supports anti-registration
by setting __enter__ = None or __exit__ = None, following the pattern
introduced in bpo-25958.

contextlib._GeneratorContextManager.__exit__ includes a special case to deal with
PEP 479 RuntimeErrors created when `StopIteration` is thrown into the context
manager body.

Previously this check was too permissive, and undid one level of chaining on *all*
RuntimeError instances, not just those that wrapped a StopIteration instance.

managed by a contextlib.ExitStack() and one of the exit stack
generators catches and raises it in a chain, do not re-raise the
original exception when exiting, let the new chained one through.
This avoids the PEP 479 bug described in issue25782.

typing.ContextManager.

Patch by Anish Shah.

keyword arguments called "func" and "self".  Patch by Martin Panter.

Raise PendingDeprecationWarning when generator raises StopIteration
and no __future__ import is used.  Fix offenders in the stdlib
and tests.

See also issue 22906.
Thanks to Nick Coghlan and Berker Peksag for reviews.

Closes issue #22906.

- Alex J Burke noticed a debugging raise in the commit that
  fixed the original bug reported in issue 20317
- this showed that multiple iterations through the affected
  loop wasn't actually being tested

- added test cases to ensure docstrings are reasonable
- also updates various comments in contextlib for accuracy
- identifed #19404 as an issue making it difficult to provide
  good help output on generator based context manager instances

- explain single use, reusable and reentrant in docs
- converted suppress to a reentrant class based impl
- converted redirect_stdout to a reusable impl
- moved both suppress and redirect_stdout behind a functional
  facade
- added reentrancy tests for the updated suppress
- added reusability tests for the updated redirect_stdio
- slightly cleaned up an exception from contextmanager

Patch by Zero Piraeus.

Report and patch by Hrvoje Nikšić

instead of manually listing tests for test.support.run_unittest().

Issue #14963: Added test cases for contextlib.ExitStack exception handling behaviour (Initial patch by Alon Horev)

Issue #11647: allow contextmanager objects to be used as decorators as described in the docs. Initial patch by Ysj Ray.

svn+ssh://pythondev@svn.python.org/python/trunk

........
  r79539 | florent.xicluna | 2010-04-01 01:01:03 +0300 (Thu, 01 Apr 2010) | 2 lines

  Replace catch_warnings with check_warnings when it makes sense.  Use assertRaises context manager to simplify some tests.
........

Issue 9110. Adding ContextDecorator to contextlib. This enables the creation of APIs that act as decorators as well as context managers. contextlib.contextmanager changed to use ContextDecorator.

svn+ssh://pythondev@svn.python.org/python/trunk

........
  r80552 | victor.stinner | 2010-04-27 23:46:03 +0200 (mar., 27 avril 2010) | 3 lines

  Issue #7449, part 1: fix test_support.py for Python compiled without thread
........
  r80553 | victor.stinner | 2010-04-27 23:47:01 +0200 (mar., 27 avril 2010) | 1 line

  Issue #7449, part 2: regrtest.py -j option requires thread support
........
  r80554 | victor.stinner | 2010-04-27 23:51:26 +0200 (mar., 27 avril 2010) | 9 lines

  Issue #7449 part 3, test_doctest: import trace module in test_coverage()

  Import trace module fail if the threading module is missing. test_coverage() is
  only used if test_doctest.py is used with the -c option. This commit allows to
  execute the test suite without thread support.

  Move "import trace" in test_coverage() and use
  test_support.import_module('trace').
........
  r80555 | victor.stinner | 2010-04-27 23:56:26 +0200 (mar., 27 avril 2010) | 6 lines

  Issue #7449, part 4: skip test_multiprocessing if thread support is disabled

  import threading after _multiprocessing to raise a more revelant error message:
  "No module named _multiprocessing". _multiprocessing is not compiled without
  thread support.
........
  r80556 | victor.stinner | 2010-04-28 00:01:24 +0200 (mer., 28 avril 2010) | 8 lines

  Issue #7449, part 5: split Test.test_open() of ctypes/test/test_errno.py

   * Split Test.test_open() in 2 functions: test_open() and test_thread_open()
   * Skip test_open() and test_thread_open() if we are unable to find the C
     library
   * Skip test_thread_open() if thread support is disabled
   * Use unittest.skipUnless(os.name == "nt", ...) on test_GetLastError()
........
  r80564 | victor.stinner | 2010-04-28 00:59:35 +0200 (mer., 28 avril 2010) | 4 lines

  Issue #7449, part 6: fix test_hashlib for missing threading module

  Move @test_support.reap_thread decorator from test_main() to test_threaded_hashing().
........
  r80565 | victor.stinner | 2010-04-28 01:01:29 +0200 (mer., 28 avril 2010) | 6 lines

  Issue #7449, part 7: simplify threading detection in test_capi

   * Skip TestPendingCalls if threading module is missing
   * Test if threading module is present or not, instead of test the presence of
     _testcapi._test_thread_state
........
  r80566 | victor.stinner | 2010-04-28 01:03:16 +0200 (mer., 28 avril 2010) | 4 lines

  Issue #7449, part 8: don't skip the whole test_asynchat if threading is missing

  TestFifo can be executed without the threading module
........
  r80568 | victor.stinner | 2010-04-28 01:14:58 +0200 (mer., 28 avril 2010) | 6 lines

  Issue #7449, part 9: fix test_xmlrpclib for missing threading module

   * Skip testcases using threads if threading module is missing
   * Use "http://" instead of URL in ServerProxyTestCase if threading is missing
     because URL is not set in this case
........
  r80569 | victor.stinner | 2010-04-28 01:33:58 +0200 (mer., 28 avril 2010) | 6 lines

  Partial revert of r80556 (Issue #7449, part 5, fix ctypes test)

  Rewrite r80556: the thread test have to be executed just after the test on
  libc_open() and so the test cannot be splitted in two functions (without
  duplicating code, and I don't want to duplicate code).
........
  r80570 | victor.stinner | 2010-04-28 01:51:16 +0200 (mer., 28 avril 2010) | 8 lines

  Issue #7449, part 10: test_cmd imports trace module using test_support.import_module()

  Use test_support.import_module() instead of import to raise a SkipTest
  exception if the import fail. Import trace fails if the threading module is
  missing.

  See also part 3: test_doctest: import trace module in test_coverage().
........
  r80571 | victor.stinner | 2010-04-28 01:55:59 +0200 (mer., 28 avril 2010) | 6 lines

  Issue #7449, last part (11): fix many tests if thread support is disabled

   * Use try/except ImportError or test_support.import_module() to import thread
     and threading modules
   * Add @unittest.skipUnless(threading, ...) to testcases using threads
........

 * Use try/except ImportError or test_support.import_module() to import thread
   and threading modules
 * Add @unittest.skipUnless(threading, ...) to testcases using threads

Merged revisions 79534,79537,79539,79558,79606 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk

........
  r79534 | florent.xicluna | 2010-03-31 23:21:54 +0200 (mer, 31 mar 2010) | 2 lines

  Fix test for xml.etree when using a non-ascii path.  And use check_warnings instead of catch_warnings.
........
  r79537 | florent.xicluna | 2010-03-31 23:40:32 +0200 (mer, 31 mar 2010) | 2 lines

  Fix typo
........
  r79539 | florent.xicluna | 2010-04-01 00:01:03 +0200 (jeu, 01 avr 2010) | 2 lines

  Replace catch_warnings with check_warnings when it makes sense.  Use assertRaises context manager to simplify some tests.
........
  r79558 | florent.xicluna | 2010-04-01 20:17:09 +0200 (jeu, 01 avr 2010) | 2 lines

  #7092: Fix some -3 warnings, and fix Lib/platform.py when the path contains a double-quote.
........
  r79606 | florent.xicluna | 2010-04-02 19:26:42 +0200 (ven, 02 avr 2010) | 2 lines

  Backport some robotparser test and skip the test if the external resource is not available.
........

Replace catch_warnings with check_warnings when it makes sense.  Use assertRaises context manager to simplify some tests.