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Merged revisions 79607-79608 via svnmerge from 

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

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  r79607 | andrew.kuchling | 2010-04-02 19:48:23 +0200 (Fr, 02 Apr 2010) | 1 line

  #6647: document that catch_warnings is not thread-safe
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  r79608 | andrew.kuchling | 2010-04-02 19:54:26 +0200 (Fr, 02 Apr 2010) | 1 line

  #6647: add note to two examples
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This commit is contained in:
Georg Brandl 2010-05-19 14:25:58 +00:00
parent 30de46c201
commit 161cdb3bfd
1 changed files with 15 additions and 2 deletions
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Doc/library/warnings.rst
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@ -178,7 +178,10 @@ the warning using the :class:`catch_warnings` context manager::
While within the context manager all warnings will simply be ignored. This
allows you to use known-deprecated code without having to see the warning while
not suppressing the warning for other code that might not be aware of its use
of deprecated code.
of deprecated code. Note: this can only be guaranteed in a single-threaded
application. If two or more threads use the :class:`catch_warnings` context
manager at the same time, the behavior is undefined.
.. _warning-testing:
@ -216,7 +219,9 @@ Once the context manager exits, the warnings filter is restored to its state
when the context was entered. This prevents tests from changing the warnings
filter in unexpected ways between tests and leading to indeterminate test
results. The :func:`showwarning` function in the module is also restored to
its original value.
its original value. Note: this can only be guaranteed in a single-threaded
application. If two or more threads use the :class:`catch_warnings` context
manager at the same time, the behavior is undefined.
When testing multiple operations that raise the same kind of warning, it
is important to test them in a manner that confirms each operation is raising
@ -356,6 +361,14 @@ Available Context Managers
protected. This argument exists primarily for testing the :mod:`warnings`
module itself.
.. note::
The :class:`catch_warnings` manager works by replacing and
then later restoring the module's
:func:`showwarning` function and internal list of filter
specifications. This means the context manager is modifying
global state and therefore is not thread-safe.
.. note::
In Python 3.0, the arguments to the constructor for