Merged revisions 66321 via svnmerge from

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

........
  r66321 | brett.cannon | 2008-09-08 17:49:16 -0700 (Mon, 08 Sep 2008) | 7 lines

  warnings.catch_warnings() now returns a list or None instead of the custom
  WarningsRecorder object. This makes the API simpler to use as no special object
  must be learned.

  Closes issue 3781.
  Review by Benjamin Peterson.
........

10 files changed, 193 insertions, 137 deletions

diff --git a/Doc/library/warnings.rst b/Doc/library/warnings.rst
index e3d3b5b..f9d01b2 100644
--- a/Doc/library/warnings.rst
+++ b/Doc/library/warnings.rst
@@ -160,6 +160,67 @@ ImportWarning can also be enabled explicitly in Python code using::
    warnings.simplefilter('default', ImportWarning)
 
 
+.. _warning-suppress:
+
+Temporarily Suppressing Warnings
+--------------------------------
+
+If you are using code that you know will raise a warning, such some deprecated
+function, but do not want to see the warning, then suppress the warning using
+the :class:`catch_warnings` context manager::
+
+    import warnings
+
+    def fxn():
+        warnings.warn("deprecated", DeprecationWarning)
+
+    with warnings.catch_warnings():
+        warnings.simplefilter("ignore")
+        fxn()
+
+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.
+
+
+.. _warning-testing:
+
+Testing Warnings
+----------------
+
+To test warnings raised by code, use the :class:`catch_warnings` context
+manager. With it you can temporarily mutate the warnings filter to facilitate
+your testing. For instance, do the following to capture all raised warnings to
+check::
+
+    import warnings
+
+    def fxn():
+        warnings.warn("deprecated", DeprecationWarning)
+
+    with warnings.catch_warnings(record=True) as w:
+        # Cause all warnings to always be triggered.
+        warnings.simplefilter("always")
+        # Trigger a warning.
+        fxn()
+        # Verify some things
+        assert len(w) == 1
+        assert isinstance(w[-1].category, DeprecationWarning)
+        assert "deprecated" in str(w[-1].message)
+
+One can also cause all warnings to be exceptions by using ``error`` instead of
+``always``. One thing to be aware of is that if a warning has already been
+raised because of a ``once``/``default`` rule, then no matter what filters are
+set the warning will not be seen again unless the warnings registry related to
+the warning has been cleared.
+
+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.
+
+
 .. _warning-functions:
 
 Available Functions
@@ -248,31 +309,22 @@ Available Functions
    and calls to :func:`simplefilter`.
 
 
-Available Classes
------------------
+Available Context Managers
+--------------------------
 
 .. class:: catch_warnings([\*, record=False, module=None])
 
-    A context manager that guards the warnings filter from being permanently
-    mutated. The manager returns an instance of :class:`WarningsRecorder`. The 
-    *record* argument specifies whether warnings that would typically be
-    handled by :func:`showwarning` should instead be recorded by the
-    :class:`WarningsRecorder` instance. This argument is typically set when
-    testing for expected warnings behavior. The *module* argument may be a
-    module object that is to be used instead of the :mod:`warnings` module.
-    This argument should only be set when testing the :mod:`warnings` module 
-    or some similar use-case.
-
-    Typical usage of the context manager is like so::
-
-        def fxn():
-            warn("fxn is deprecated", DeprecationWarning)
-            return "spam spam bacon spam"
+    A context manager that copies and, upon exit, restores the warnings filter.
+    If the *record* argument is False (the default) the context manager returns
+    :class:`None`. If *record* is true, a list is returned that is populated
+    with objects as seen by a custom :func:`showwarning` function (which also
+    suppresses output to ``sys.stdout``). Each object has attributes with the
+    same names as the arguments to :func:`showwarning`.
 
-        # The function 'fxn' is known to raise a DeprecationWarning.
-        with catch_warnings() as w:
-            warnings.filterwarning('ignore', 'fxn is deprecated', DeprecationWarning)
-            fxn()  # DeprecationWarning is temporarily suppressed.
+    The *module* argument takes a module that will be used instead of the
+    module returned when you import :mod:`warnings` whose filter will be
+    protected. This arguments exists primarily for testing the :mod:`warnings`
+    module itself.
 
     .. versionadded:: 2.6
 
@@ -280,19 +332,3 @@ Available Classes
 
        Constructor arguments turned into keyword-only arguments.
 
-
-.. class:: WarningsRecorder()
-
-    A subclass of :class:`list` that stores all warnings passed to
-    :func:`showwarning` when returned by a :class:`catch_warnings` context
-    manager created with its *record* argument set to ``True``. Each recorded
-    warning is represented by an object whose attributes correspond to the
-    arguments to :func:`showwarning`. As a convenience, a
-    :class:`WarningsRecorder` instance has the attributes of the last
-    recorded warning set on the :class:`WarningsRecorder` instance as well.
-
-    .. method:: reset()
-
-        Delete all recorded warnings.
-
-    .. versionadded:: 2.6
diff --git a/Lib/test/test___all__.py b/Lib/test/test___all__.py
index ba8f75b..052cc20 100644
--- a/Lib/test/test___all__.py
+++ b/Lib/test/test___all__.py
@@ -1,5 +1,5 @@
 import unittest
-from test.support import run_unittest, catch_warning
+from test.support import run_unittest
 import sys
 import warnings
 
@@ -8,7 +8,7 @@ class AllTest(unittest.TestCase):
 
     def check_all(self, modname):
         names = {}
-        with catch_warning():
+        with warnings.catch_warnings():
             warnings.filterwarnings("ignore", ".* (module|package)",
                                     DeprecationWarning)
             try:
diff --git a/Lib/test/test_hmac.py b/Lib/test/test_hmac.py
index 43953cf..f7ac8ef 100644
--- a/Lib/test/test_hmac.py
+++ b/Lib/test/test_hmac.py
@@ -211,7 +211,7 @@ class TestVectorsTestCase(unittest.TestCase):
             def digest(self):
                 return self._x.digest()
 
-        with support.catch_warning():
+        with warnings.catch_warnings():
             warnings.simplefilter('error', RuntimeWarning)
             try:
                 hmac.HMAC(b'a', b'b', digestmod=MockCrazyHash)
diff --git a/Lib/test/test_import.py b/Lib/test/test_import.py
index aa65c7a..0dbbbf0 100644
--- a/Lib/test/test_import.py
+++ b/Lib/test/test_import.py
@@ -6,7 +6,7 @@ import sys
 import py_compile
 import warnings
 import imp
-from test.support import unlink, TESTFN, unload, run_unittest, catch_warning
+from test.support import unlink, TESTFN, unload, run_unittest
 
 
 def remove_files(name):
@@ -153,7 +153,7 @@ class ImportTest(unittest.TestCase):
         self.assert_(y is test.support, y.__name__)
 
     def test_import_initless_directory_warning(self):
-        with catch_warning():
+        with warnings.catch_warnings():
             # Just a random non-package directory we always expect to be
             # somewhere in sys.path...
             warnings.simplefilter('error', ImportWarning)
diff --git a/Lib/test/test_re.py b/Lib/test/test_re.py
index 17370bb..6ee84c6 100644
--- a/Lib/test/test_re.py
+++ b/Lib/test/test_re.py
@@ -1,7 +1,7 @@
 import sys
 sys.path = ['.'] + sys.path
 
-from test.support import verbose, run_unittest, catch_warning
+from test.support import verbose, run_unittest
 import re
 from re import Scanner
 import sys, os, traceback
diff --git a/Lib/test/test_struct.py b/Lib/test/test_struct.py
index 6dc0e8d..00219b8 100644
--- a/Lib/test/test_struct.py
+++ b/Lib/test/test_struct.py
@@ -4,7 +4,7 @@ import struct
 import warnings
 
 from functools import wraps
-from test.support import TestFailed, verbose, run_unittest, catch_warning
+from test.support import TestFailed, verbose, run_unittest
 
 import sys
 ISBIGENDIAN = sys.byteorder == "big"
@@ -34,7 +34,7 @@ def bigendian_to_native(value):
 def with_warning_restore(func):
     @wraps(func)
     def decorator(*args, **kw):
-        with catch_warning():
+        with warnings.catch_warnings():
             # We need this function to warn every time, so stick an
             # unqualifed 'always' at the head of the filter list
             warnings.simplefilter("always")
diff --git a/Lib/test/test_structmembers.py b/Lib/test/test_structmembers.py
index d6c9fea..878223a 100644
--- a/Lib/test/test_structmembers.py
+++ b/Lib/test/test_structmembers.py
@@ -66,35 +66,35 @@ class ReadWriteTests(unittest.TestCase):
 
 class TestWarnings(unittest.TestCase):
     def has_warned(self, w):
-        self.assertEqual(w.category, RuntimeWarning)
+        self.assertEqual(w[-1].category, RuntimeWarning)
 
     def test_byte_max(self):
-        with support.catch_warning() as w:
+        with warnings.catch_warnings(record=True) as w:
             ts.T_BYTE = CHAR_MAX+1
             self.has_warned(w)
 
     def test_byte_min(self):
-        with support.catch_warning() as w:
+        with warnings.catch_warnings(record=True) as w:
             ts.T_BYTE = CHAR_MIN-1
             self.has_warned(w)
 
     def test_ubyte_max(self):
-        with support.catch_warning() as w:
+        with warnings.catch_warnings(record=True) as w:
             ts.T_UBYTE = UCHAR_MAX+1
             self.has_warned(w)
 
     def test_short_max(self):
-        with support.catch_warning() as w:
+        with warnings.catch_warnings(record=True) as w:
             ts.T_SHORT = SHRT_MAX+1
             self.has_warned(w)
 
     def test_short_min(self):
-        with support.catch_warning() as w:
+        with warnings.catch_warnings(record=True) as w:
             ts.T_SHORT = SHRT_MIN-1
             self.has_warned(w)
 
     def test_ushort_max(self):
-        with support.catch_warning() as w:
+        with warnings.catch_warnings(record=True) as w:
             ts.T_USHORT = USHRT_MAX+1
             self.has_warned(w)
 
diff --git a/Lib/test/test_sundry.py b/Lib/test/test_sundry.py
index a99d2c0..6b425c6 100644
--- a/Lib/test/test_sundry.py
+++ b/Lib/test/test_sundry.py
@@ -7,7 +7,7 @@ import warnings
 
 class TestUntestedModules(unittest.TestCase):
     def test_at_least_import_untested_modules(self):
-        with support.catch_warning():
+        with warnings.catch_warnings(record=True):
             import aifc
             import bdb
             import cgitb
diff --git a/Lib/test/test_warnings.py b/Lib/test/test_warnings.py
index 087bf3d..199e6fc 100644
--- a/Lib/test/test_warnings.py
+++ b/Lib/test/test_warnings.py
@@ -72,64 +72,69 @@ class FilterTests(object):
     """Testing the filtering functionality."""
 
     def test_error(self):
-        with support.catch_warning(self.module) as w:
+        with original_warnings.catch_warnings(module=self.module) as w:
             self.module.resetwarnings()
             self.module.filterwarnings("error", category=UserWarning)
             self.assertRaises(UserWarning, self.module.warn,
                                 "FilterTests.test_error")
 
     def test_ignore(self):
-        with support.catch_warning(module=self.module) as w:
+        with original_warnings.catch_warnings(record=True,
+                module=self.module) as w:
             self.module.resetwarnings()
             self.module.filterwarnings("ignore", category=UserWarning)
             self.module.warn("FilterTests.test_ignore", UserWarning)
             self.assertEquals(len(w), 0)
 
     def test_always(self):
-        with support.catch_warning(module=self.module) as w:
+        with original_warnings.catch_warnings(record=True,
+                module=self.module) as w:
             self.module.resetwarnings()
             self.module.filterwarnings("always", category=UserWarning)
             message = "FilterTests.test_always"
             self.module.warn(message, UserWarning)
-            self.assert_(message, w.message)
+            self.assert_(message, w[-1].message)
             self.module.warn(message, UserWarning)
-            self.assert_(w.message, message)
+            self.assert_(w[-1].message, message)
 
     def test_default(self):
-        with support.catch_warning(self.module) as w:
+        with original_warnings.catch_warnings(record=True,
+                module=self.module) as w:
             self.module.resetwarnings()
             self.module.filterwarnings("default", category=UserWarning)
             message = UserWarning("FilterTests.test_default")
             for x in range(2):
                 self.module.warn(message, UserWarning)
                 if x == 0:
-                    self.assertEquals(w.message, message)
-                    w.reset()
+                    self.assertEquals(w[-1].message, message)
+                    del w[:]
                 elif x == 1:
-                    self.assert_(not len(w), "unexpected warning: " + str(w))
+                    self.assertEquals(len(w), 0)
                 else:
                     raise ValueError("loop variant unhandled")
 
     def test_module(self):
-        with support.catch_warning(self.module) as w:
+        with original_warnings.catch_warnings(record=True,
+                module=self.module) as w:
             self.module.resetwarnings()
             self.module.filterwarnings("module", category=UserWarning)
             message = UserWarning("FilterTests.test_module")
             self.module.warn(message, UserWarning)
-            self.assertEquals(w.message, message)
-            w.reset()
+            self.assertEquals(w[-1].message, message)
+            del w[:]
             self.module.warn(message, UserWarning)
-            self.assert_(not len(w), "unexpected message: " + str(w))
+            self.assertEquals(len(w), 0)
 
     def test_once(self):
-        with support.catch_warning(self.module) as w:
+        with original_warnings.catch_warnings(record=True,
+                module=self.module) as w:
             self.module.resetwarnings()
             self.module.filterwarnings("once", category=UserWarning)
             message = UserWarning("FilterTests.test_once")
             self.module.warn_explicit(message, UserWarning, "test_warnings.py",
                                     42)
-            self.assertEquals(w.message, message)
-            w.reset()
+            self.assertEquals(w[-1].message, message)
+            del w[:]
             self.module.warn_explicit(message, UserWarning, "test_warnings.py",
                                     13)
             self.assertEquals(len(w), 0)
@@ -138,19 +143,20 @@ class FilterTests(object):
             self.assertEquals(len(w), 0)
 
     def test_inheritance(self):
-        with support.catch_warning(self.module) as w:
+        with original_warnings.catch_warnings(module=self.module) as w:
             self.module.resetwarnings()
             self.module.filterwarnings("error", category=Warning)
             self.assertRaises(UserWarning, self.module.warn,
                                 "FilterTests.test_inheritance", UserWarning)
 
     def test_ordering(self):
-        with support.catch_warning(self.module) as w:
+        with original_warnings.catch_warnings(record=True,
+                module=self.module) as w:
             self.module.resetwarnings()
             self.module.filterwarnings("ignore", category=UserWarning)
             self.module.filterwarnings("error", category=UserWarning,
                                         append=True)
-            w.reset()
+            del w[:]
             try:
                 self.module.warn("FilterTests.test_ordering", UserWarning)
             except UserWarning:
@@ -160,28 +166,29 @@ class FilterTests(object):
     def test_filterwarnings(self):
         # Test filterwarnings().
         # Implicitly also tests resetwarnings().
-        with support.catch_warning(self.module) as w:
+        with original_warnings.catch_warnings(record=True,
+                module=self.module) as w:
             self.module.filterwarnings("error", "", Warning, "", 0)
             self.assertRaises(UserWarning, self.module.warn, 'convert to error')
 
             self.module.resetwarnings()
             text = 'handle normally'
             self.module.warn(text)
-            self.assertEqual(str(w.message), text)
-            self.assert_(w.category is UserWarning)
+            self.assertEqual(str(w[-1].message), text)
+            self.assert_(w[-1].category is UserWarning)
 
             self.module.filterwarnings("ignore", "", Warning, "", 0)
             text = 'filtered out'
             self.module.warn(text)
-            self.assertNotEqual(str(w.message), text)
+            self.assertNotEqual(str(w[-1].message), text)
 
             self.module.resetwarnings()
             self.module.filterwarnings("error", "hex*", Warning, "", 0)
             self.assertRaises(UserWarning, self.module.warn, 'hex/oct')
             text = 'nonmatching text'
             self.module.warn(text)
-            self.assertEqual(str(w.message), text)
-            self.assert_(w.category is UserWarning)
+            self.assertEqual(str(w[-1].message), text)
+            self.assert_(w[-1].category is UserWarning)
 
 class CFilterTests(BaseTest, FilterTests):
     module = c_warnings
@@ -195,12 +202,13 @@ class WarnTests(unittest.TestCase):
     """Test warnings.warn() and warnings.warn_explicit()."""
 
     def test_message(self):
-        with support.catch_warning(self.module) as w:
+        with original_warnings.catch_warnings(record=True,
+                module=self.module) as w:
             for i in range(4):
                 text = 'multi %d' %i  # Different text on each call.
                 self.module.warn(text)
-                self.assertEqual(str(w.message), text)
-                self.assert_(w.category is UserWarning)
+                self.assertEqual(str(w[-1].message), text)
+                self.assert_(w[-1].category is UserWarning)
 
     # Issue 3639
     def test_warn_nonstandard_types(self):
@@ -210,35 +218,45 @@ class WarnTests(unittest.TestCase):
                 self.module.warn(ob)
                 # Don't directly compare objects since
                 # ``Warning() != Warning()``.
-                self.assertEquals(str(w.message), str(UserWarning(ob)))
+                self.assertEquals(str(w[-1].message), str(UserWarning(ob)))
 
     def test_filename(self):
         with warnings_state(self.module):
-            with support.catch_warning(self.module) as w:
+            with original_warnings.catch_warnings(record=True,
+                    module=self.module) as w:
                 warning_tests.inner("spam1")
-                self.assertEqual(os.path.basename(w.filename), "warning_tests.py")
+                self.assertEqual(os.path.basename(w[-1].filename),
+                                    "warning_tests.py")
                 warning_tests.outer("spam2")
-                self.assertEqual(os.path.basename(w.filename), "warning_tests.py")
+                self.assertEqual(os.path.basename(w[-1].filename),
+                                    "warning_tests.py")
 
     def test_stacklevel(self):
         # Test stacklevel argument
         # make sure all messages are different, so the warning won't be skipped
         with warnings_state(self.module):
-            with support.catch_warning(self.module) as w:
+            with original_warnings.catch_warnings(record=True,
+                    module=self.module) as w:
                 warning_tests.inner("spam3", stacklevel=1)
-                self.assertEqual(os.path.basename(w.filename), "warning_tests.py")
+                self.assertEqual(os.path.basename(w[-1].filename),
+                                    "warning_tests.py")
                 warning_tests.outer("spam4", stacklevel=1)
-                self.assertEqual(os.path.basename(w.filename), "warning_tests.py")
+                self.assertEqual(os.path.basename(w[-1].filename),
+                                    "warning_tests.py")
 
                 warning_tests.inner("spam5", stacklevel=2)
-                self.assertEqual(os.path.basename(w.filename), "test_warnings.py")
+                self.assertEqual(os.path.basename(w[-1].filename),
+                                    "test_warnings.py")
                 warning_tests.outer("spam6", stacklevel=2)
-                self.assertEqual(os.path.basename(w.filename), "warning_tests.py")
+                self.assertEqual(os.path.basename(w[-1].filename),
+                                    "warning_tests.py")
                 warning_tests.outer("spam6.5", stacklevel=3)
-                self.assertEqual(os.path.basename(w.filename), "test_warnings.py")
+                self.assertEqual(os.path.basename(w[-1].filename),
+                                    "test_warnings.py")
 
                 warning_tests.inner("spam7", stacklevel=9999)
-                self.assertEqual(os.path.basename(w.filename), "sys")
+                self.assertEqual(os.path.basename(w[-1].filename),
+                                    "sys")
 
     def test_missing_filename_not_main(self):
         # If __file__ is not specified and __main__ is not the module name,
@@ -247,9 +265,10 @@ class WarnTests(unittest.TestCase):
         try:
             del warning_tests.__file__
             with warnings_state(self.module):
-                with support.catch_warning(self.module) as w:
+                with original_warnings.catch_warnings(record=True,
+                        module=self.module) as w:
                     warning_tests.inner("spam8", stacklevel=1)
-                    self.assertEqual(w.filename, warning_tests.__name__)
+                    self.assertEqual(w[-1].filename, warning_tests.__name__)
         finally:
             warning_tests.__file__ = filename
 
@@ -264,9 +283,10 @@ class WarnTests(unittest.TestCase):
             del warning_tests.__file__
             warning_tests.__name__ = '__main__'
             with warnings_state(self.module):
-                with support.catch_warning(self.module) as w:
+                with original_warnings.catch_warnings(record=True,
+                        module=self.module) as w:
                     warning_tests.inner('spam9', stacklevel=1)
-                    self.assertEqual(w.filename, sys.argv[0])
+                    self.assertEqual(w[-1].filename, sys.argv[0])
         finally:
             warning_tests.__file__ = filename
             warning_tests.__name__ = module_name
@@ -282,9 +302,10 @@ class WarnTests(unittest.TestCase):
             warning_tests.__name__ = '__main__'
             del sys.argv
             with warnings_state(self.module):
-                with support.catch_warning(self.module) as w:
+                with original_warnings.catch_warnings(record=True,
+                        module=self.module) as w:
                     warning_tests.inner('spam10', stacklevel=1)
-                    self.assertEqual(w.filename, '__main__')
+                    self.assertEqual(w[-1].filename, '__main__')
         finally:
             warning_tests.__file__ = filename
             warning_tests.__name__ = module_name
@@ -302,9 +323,10 @@ class WarnTests(unittest.TestCase):
             warning_tests.__name__ = '__main__'
             sys.argv = ['']
             with warnings_state(self.module):
-                with support.catch_warning(self.module) as w:
+                with original_warnings.catch_warnings(record=True,
+                        module=self.module) as w:
                     warning_tests.inner('spam11', stacklevel=1)
-                    self.assertEqual(w.filename, '__main__')
+                    self.assertEqual(w[-1].filename, '__main__')
         finally:
             warning_tests.__file__ = file_name
             warning_tests.__name__ = module_name
@@ -337,7 +359,7 @@ class WCmdLineTests(unittest.TestCase):
     def test_improper_input(self):
         # Uses the private _setoption() function to test the parsing
         # of command-line warning arguments
-        with support.catch_warning(self.module):
+        with original_warnings.catch_warnings(module=self.module):
             self.assertRaises(self.module._OptionError,
                               self.module._setoption, '1:2:3:4:5:6')
             self.assertRaises(self.module._OptionError,
@@ -362,7 +384,7 @@ class _WarningsTests(BaseTest):
 
     def test_filter(self):
         # Everything should function even if 'filters' is not in warnings.
-        with support.catch_warning(self.module) as w:
+        with original_warnings.catch_warnings(module=self.module) as w:
             self.module.filterwarnings("error", "", Warning, "", 0)
             self.assertRaises(UserWarning, self.module.warn,
                                 'convert to error')
@@ -377,21 +399,22 @@ class _WarningsTests(BaseTest):
         try:
             original_registry = self.module.onceregistry
             __warningregistry__ = {}
-            with support.catch_warning(self.module) as w:
+            with original_warnings.catch_warnings(record=True,
+                    module=self.module) as w:
                 self.module.resetwarnings()
                 self.module.filterwarnings("once", category=UserWarning)
                 self.module.warn_explicit(message, UserWarning, "file", 42)
-                self.failUnlessEqual(w.message, message)
-                w.reset()
+                self.failUnlessEqual(w[-1].message, message)
+                del w[:]
                 self.module.warn_explicit(message, UserWarning, "file", 42)
                 self.assertEquals(len(w), 0)
                 # Test the resetting of onceregistry.
                 self.module.onceregistry = {}
                 __warningregistry__ = {}
                 self.module.warn('onceregistry test')
-                self.failUnlessEqual(w.message.args, message.args)
+                self.failUnlessEqual(w[-1].message.args, message.args)
                 # Removal of onceregistry is okay.
-                w.reset()
+                del w[:]
                 del self.module.onceregistry
                 __warningregistry__ = {}
                 self.module.warn_explicit(message, UserWarning, "file", 42)
@@ -402,7 +425,7 @@ class _WarningsTests(BaseTest):
     def test_showwarning_missing(self):
         # Test that showwarning() missing is okay.
         text = 'del showwarning test'
-        with support.catch_warning(self.module):
+        with original_warnings.catch_warnings(module=self.module):
             self.module.filterwarnings("always", category=UserWarning)
             del self.module.showwarning
             with support.captured_output('stderr') as stream:
@@ -423,7 +446,7 @@ class _WarningsTests(BaseTest):
     def test_show_warning_output(self):
         # With showarning() missing, make sure that output is okay.
         text = 'test show_warning'
-        with support.catch_warning(self.module):
+        with original_warnings.catch_warnings(module=self.module):
             self.module.filterwarnings("always", category=UserWarning)
             del self.module.showwarning
             with support.captured_output('stderr') as stream:
@@ -494,6 +517,7 @@ class CWarningsDisplayTests(BaseTest, WarningsDisplayTests):
 class PyWarningsDisplayTests(BaseTest, WarningsDisplayTests):
     module = py_warnings
 
+
 class CatchWarningTests(BaseTest):
 
     """Test catch_warnings()."""
@@ -517,12 +541,12 @@ class CatchWarningTests(BaseTest):
             self.assertEqual(w, [])
             wmod.simplefilter("always")
             wmod.warn("foo")
-            self.assertEqual(str(w.message), "foo")
+            self.assertEqual(str(w[-1].message), "foo")
             wmod.warn("bar")
-            self.assertEqual(str(w.message), "bar")
+            self.assertEqual(str(w[-1].message), "bar")
             self.assertEqual(str(w[0].message), "foo")
             self.assertEqual(str(w[1].message), "bar")
-            w.reset()
+            del w[:]
             self.assertEqual(w, [])
         orig_showwarning = wmod.showwarning
         with support.catch_warning(module=wmod, record=False) as w:
diff --git a/Lib/warnings.py b/Lib/warnings.py
index 566e0b9..0e147db 100644
--- a/Lib/warnings.py
+++ b/Lib/warnings.py
@@ -7,7 +7,7 @@ import linecache
 import sys
 
 __all__ = ["warn", "showwarning", "formatwarning", "filterwarnings",
-           "resetwarnings"]
+           "resetwarnings", "catch_warnings"]
 
 
 def showwarning(message, category, filename, lineno, file=None, line=None):
@@ -274,28 +274,20 @@ class WarningMessage(object):
                                     self.filename, self.lineno, self.line))
 
 
-class WarningsRecorder(list):
-
-    """Record the result of various showwarning() calls."""
-
-    def showwarning(self, *args, **kwargs):
-        self.append(WarningMessage(*args, **kwargs))
-
-    def __getattr__(self, attr):
-        return getattr(self[-1], attr)
-
-    def reset(self):
-        del self[:]
-
-
 class catch_warnings(object):
 
-    """Guard the warnings filter from being permanently changed and optionally
-    record the details of any warnings that are issued.
+    """A context manager that copies and restores the warnings filter upon
+    exiting the context.
+
+    The 'record' argument specifies whether warnings should be captured by a
+    custom implementation of warnings.showwarning() and be appended to a list
+    returned by the context manager. Otherwise None is returned by the context
+    manager. The objects appended to the list are arguments whose attributes
+    mirror the arguments to showwarning().
 
-    Context manager returns an instance of warnings.WarningRecorder which is a
-    list of WarningMessage instances. Attributes on WarningRecorder are
-    redirected to the last created WarningMessage instance.
+    The 'module' argument is to specify an alternative module to the module
+    named 'warnings' and imported under that name. This argument is only useful
+    when testing the warnings module itself.
 
     """
 
@@ -307,17 +299,21 @@ class catch_warnings(object):
         keyword-only.
 
         """
-        self._recorder = WarningsRecorder() if record else None
+        self._record = record
         self._module = sys.modules['warnings'] if module is None else module
 
     def __enter__(self):
         self._filters = self._module.filters
         self._module.filters = self._filters[:]
         self._showwarning = self._module.showwarning
-        if self._recorder is not None:
-            self._recorder.reset()  # In case the instance is being reused.
-            self._module.showwarning = self._recorder.showwarning
-        return self._recorder
+        if self._record:
+            log = []
+            def showwarning(*args, **kwargs):
+                log.append(WarningMessage(*args, **kwargs))
+            self._module.showwarning = showwarning
+            return log
+        else:
+            return None
 
     def __exit__(self, *exc_info):
         self._module.filters = self._filters