[Python-checkins] bpo-29620: iterate over a copy of sys.modules (GH-4800) (GH-20816)

[Miss Islington (bot)]

https://github.com/python/cpython/commit/3e499cda47afe2282ca3f1d04151e2c86f2e7e09
commit: 3e499cda47afe2282ca3f1d04151e2c86f2e7e09
branch: 3.8
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: GitHub <noreply at github.com>
date: 2020-06-11T14:31:46-04:00
summary:

bpo-29620: iterate over a copy of sys.modules (GH-4800) (GH-20816)

unittest.TestCase.assertWarns no longer raises a RuntimeException
when accessing a module's ``__warningregistry__`` causes importation of a new
module, or when a new module is imported in another thread.
(cherry picked from commit 46398fba4d66ad342cf2504ef947b5fb857423b2)

Co-authored-by: kernc <kerncece at gmail.com>

files:
A Misc/NEWS.d/next/Library/2018-08-21-16-20-33.bpo-29620.xxx666.rst
M Lib/unittest/case.py
M Lib/unittest/test/test_case.py

diff --git a/Lib/unittest/case.py b/Lib/unittest/case.py
index e5734b6b7a298..3223c0bff6fa2 100644
--- a/Lib/unittest/case.py
+++ b/Lib/unittest/case.py
@@ -251,7 +251,7 @@ class _AssertWarnsContext(_AssertRaisesBaseContext):
     def __enter__(self):
         # The __warningregistry__'s need to be in a pristine state for tests
         # to work properly.
-        for v in sys.modules.values():
+        for v in list(sys.modules.values()):
             if getattr(v, '__warningregistry__', None):
                 v.__warningregistry__ = {}
         self.warnings_manager = warnings.catch_warnings(record=True)
diff --git a/Lib/unittest/test/test_case.py b/Lib/unittest/test/test_case.py
index f855c4dc00b31..3dedcbe6aad5f 100644
--- a/Lib/unittest/test/test_case.py
+++ b/Lib/unittest/test/test_case.py
@@ -8,6 +8,7 @@
 import warnings
 import weakref
 import inspect
+import types
 
 from copy import deepcopy
 from test import support
@@ -1350,6 +1351,20 @@ class MyWarn(Warning):
             pass
         self.assertRaises(TypeError, self.assertWarnsRegex, MyWarn, lambda: True)
 
+    def testAssertWarnsModifySysModules(self):
+        # bpo-29620: handle modified sys.modules during iteration
+        class Foo(types.ModuleType):
+            @property
+            def __warningregistry__(self):
+                sys.modules['@bar@'] = 'bar'
+
+        sys.modules['@foo@'] = Foo('foo')
+        try:
+            self.assertWarns(UserWarning, warnings.warn, 'expected')
+        finally:
+            del sys.modules['@foo@']
+            del sys.modules['@bar@']
+
     def testAssertRaisesRegexMismatch(self):
         def Stub():
             raise Exception('Unexpected')
diff --git a/Misc/NEWS.d/next/Library/2018-08-21-16-20-33.bpo-29620.xxx666.rst b/Misc/NEWS.d/next/Library/2018-08-21-16-20-33.bpo-29620.xxx666.rst
new file mode 100644
index 0000000000000..d781919504e68
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2018-08-21-16-20-33.bpo-29620.xxx666.rst
@@ -0,0 +1,3 @@
+:func:`~unittest.TestCase.assertWarns` no longer raises a ``RuntimeException``
+when accessing a module's ``__warningregistry__`` causes importation of a new
+module, or when a new module is imported in another thread. Patch by Kernc.