bpo-33169: Remove values of `None` from sys.path_importer_cache when invalidating caches (GH-6402)

An entry of None in sys.path_importer_cache represents a negative/missing finder for a path, so clearing it out makes sense.

2 files changed, 22 insertions, 1 deletions

diff --git a/Lib/test/test_importlib/import_/test_path.py b/Lib/test/test_importlib/import_/test_path.py
index 7aa26b0eee7..18c81dda45c 100644
--- a/Lib/test/test_importlib/import_/test_path.py
+++ b/Lib/test/test_importlib/import_/test_path.py
@@ -184,6 +184,27 @@ class FinderTests:
             # Do not want FileNotFoundError raised.
             self.assertIsNone(self.machinery.PathFinder.find_spec('whatever'))
 
+    def test_invalidate_caches_finders(self):
+        # Finders with an invalidate_caches() method have it called.
+        class FakeFinder:
+            def __init__(self):
+                self.called = False
+
+            def invalidate_caches(self):
+                self.called = True
+
+        cache = {'leave_alone': object(), 'finder_to_invalidate': FakeFinder()}
+        with util.import_state(path_importer_cache=cache):
+            self.machinery.PathFinder.invalidate_caches()
+        self.assertTrue(cache['finder_to_invalidate'].called)
+
+    def test_invalidate_caches_clear_out_None(self):
+        # Clear out None in sys.path_importer_cache() when invalidating caches.
+        cache = {'clear_out': None}
+        with util.import_state(path_importer_cache=cache):
+            self.machinery.PathFinder.invalidate_caches()
+        self.assertEqual(len(cache), 0)
+
 
 class FindModuleTests(FinderTests):
     def find(self, *args, **kwargs):
diff --git a/Lib/test/test_importlib/test_api.py b/Lib/test/test_importlib/test_api.py
index 8beb4244eac..edb745c2cd4 100644
--- a/Lib/test/test_importlib/test_api.py
+++ b/Lib/test/test_importlib/test_api.py
@@ -406,7 +406,7 @@ class InvalidateCacheTests:
         # There should be no issues if the method is not defined.
         key = 'gobbledeegook'
         sys.path_importer_cache[key] = None
-        self.addCleanup(lambda: sys.path_importer_cache.__delitem__(key))
+        self.addCleanup(lambda: sys.path_importer_cache.pop(key, None))
         self.init.invalidate_caches()  # Shouldn't trigger an exception.