Fixed #14698 -- Ensure that module_has_sumodule doesn't mistake a cache miss for…

Fixed #14698 -- Ensure that module_has_sumodule doesn't mistake a cache miss for an existent package. Thanks to Łukasz Rekucki for the report and patch, and to shields for the test case.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15362 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/utils/module_loading.py

@@ -6,8 +6,11 @@ import sys
 def module_has_submodule(package, module_name):
     """See if 'module' is in 'package'."""
     name = ".".join([package.__name__, module_name])
-    if name in sys.modules:
-        return True
+    try:
+        # None indicates a cached miss; see mark_miss() in Python/import.c.
+        return sys.modules[name] is not None
+    except KeyError:
+        pass
     for finder in sys.meta_path:
         if finder.find_module(name):
             return True

tests/regressiontests/utils/module_loading.py

@@ -25,6 +25,10 @@ class DefaultLoader(unittest.TestCase):
         self.assertFalse(module_has_submodule(test_module, 'no_such_module'))
         self.assertRaises(ImportError, import_module, 'regressiontests.utils.test_module.no_such_module')
 
+        # Don't be confused by caching of import misses
+        import types  # causes attempted import of regressiontests.utils.types
+        self.assertFalse(module_has_submodule(sys.modules['regressiontests.utils'], 'types'))
+
 class EggLoader(unittest.TestCase):
     def setUp(self):
         self.old_path = sys.path[:]