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.

1 files changed, 4 insertions, 2 deletions

diff --git a/Lib/importlib/_bootstrap_external.py b/Lib/importlib/_bootstrap_external.py
index 420ecc8..da9a75c 100644
--- a/Lib/importlib/_bootstrap_external.py
+++ b/Lib/importlib/_bootstrap_external.py
@@ -1181,8 +1181,10 @@ class PathFinder:
     def invalidate_caches(cls):
         """Call the invalidate_caches() method on all path entry finders
         stored in sys.path_importer_caches (where implemented)."""
-        for finder in sys.path_importer_cache.values():
-            if hasattr(finder, 'invalidate_caches'):
+        for name, finder in list(sys.path_importer_cache.items()):
+            if finder is None:
+                del sys.path_importer_cache[name]
+            elif hasattr(finder, 'invalidate_caches'):
                 finder.invalidate_caches()
 
     @classmethod