prefer clearing global objects to obscure module.__dict__ bugs #10068

diff --git a/Doc/reference/datamodel.rst b/Doc/reference/datamodel.rst
index 9d084cf191fcc22e3734a4b98bc20af3f25417df..d3b2c15b579fae82358104c9e79ef74bb0bb4bf4 100644 (file)
--- a/Doc/reference/datamodel.rst
+++ b/Doc/reference/datamodel.rst
@@ -654,6 +654,13 @@ Modules
    Special read-only attribute: :attr:`__dict__` is the module's namespace as a
    dictionary object.
 
+   .. impl-detail::
+
+      Because of the way CPython clears module dictionaries, the module
+      dictionary will be cleared when the module falls out of scope even if the
+      dictionary still has live references.  To avoid this, copy the dictionary
+      or keep the module around while using its dictionary directly.
+
    .. index::
       single: __name__ (module attribute)
       single: __doc__ (module attribute)

diff --git a/Lib/test/test_module.py b/Lib/test/test_module.py
index 21ddc9af6fe0a5ca24e7eb078969a88538c8c350..7734fb04a260e694b7241704b36a3ae872296458 100644 (file)
--- a/Lib/test/test_module.py
+++ b/Lib/test/test_module.py
@@ -1,6 +1,6 @@
 # Test the module type
 import unittest
-from test.support import run_unittest
+from test.support import run_unittest, gc_collect
 
 import sys
 ModuleType = type(sys)
@@ -55,14 +55,29 @@ class ModuleTests(unittest.TestCase):
               {"__name__": "foo", "__doc__": "foodoc", "bar": 42})
         self.assertTrue(foo.__dict__ is d)
 
+    @unittest.expectedFailure
     def test_dont_clear_dict(self):
         # See issue 7140.
         def f():
             foo = ModuleType("foo")
             foo.bar = 4
             return foo
+        gc_collect()
         self.assertEqual(f().__dict__["bar"], 4)
 
+    def test_clear_dict_in_ref_cycle(self):
+        destroyed = []
+        m = ModuleType("foo")
+        m.destroyed = destroyed
+        s = """class A:
+    def __del__(self):
+        destroyed.append(1)
+a = A()"""
+        exec(s, m.__dict__)
+        del m
+        gc_collect()
+        self.assertEqual(destroyed, [1])
+
 def test_main():
     run_unittest(ModuleTests)
 

diff --git a/Misc/NEWS b/Misc/NEWS
index 8ff3f3b1ee926e98c8582a1b27d56bb44f028c90..0b7d77cdf8fe0c3d4c9622edbba9616275ea7463 100644 (file)
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -37,6 +37,9 @@ What's New in Python 3.2 Alpha 3?
 Core and Builtins
 -----------------
 
+- Issue #10068: Global objects which have reference cycles with their module's
+  dict are now cleared again. This causes issue #7140 to appear again.
+
 - Issue #9738: Document PyErr_SetString() and PyErr_SetFromErrnoWithFilename()
   encodings.
 

diff --git a/Objects/moduleobject.c b/Objects/moduleobject.c
index 3a9526102825faa50756b89b6fd3776ea0055451..1e3349d0a3581706067f85e53a634a73153d631f 100644 (file)
--- a/Objects/moduleobject.c
+++ b/Objects/moduleobject.c
@@ -335,10 +335,7 @@ module_dealloc(PyModuleObject *m)
     if (m->md_def && m->md_def->m_free)
         m->md_def->m_free(m);
     if (m->md_dict != NULL) {
-        /* If we are the only ones holding a reference, we can clear
-           the dictionary. */
-        if (Py_REFCNT(m->md_dict) == 1)
-            _PyModule_Clear((PyObject *)m);
+        _PyModule_Clear((PyObject *)m);
         Py_DECREF(m->md_dict);
     }
     if (m->md_state != NULL)