Fix bug in __import__ during Python shutdown

Issue #26637: The importlib module now emits an ImportError rather than a
TypeError if __import__() is tried during the Python shutdown process but
sys.path is already cleared (set to None).

Author: vstinner

Lib/importlib/_bootstrap.py

@@ -878,13 +878,20 @@ def _find_spec_legacy(finder, name, path):
 
 def _find_spec(name, path, target=None):
     """Find a module's loader."""
-    if sys.meta_path is not None and not sys.meta_path:
+    meta_path = sys.meta_path
+    if meta_path is None:
+        # PyImport_Cleanup() is running or has been called.
+        raise ImportError("sys.meta_path is None, Python is likely "
+                          "shutting down")
+
+    if not meta_path:
         _warnings.warn('sys.meta_path is empty', ImportWarning)
+
     # We check sys.modules here for the reload case.  While a passed-in
     # target will usually indicate a reload there is no guarantee, whereas
     # sys.modules provides one.
     is_reload = name in sys.modules
-    for finder in sys.meta_path:
+    for finder in meta_path:
         with _ImportLockContext():
             try:
                 find_spec = finder.find_spec

Misc/NEWS

@@ -232,6 +232,11 @@ Core and Builtins
 Library
 -------
 
+- Issue #26637: The :mod:`importlib` module now emits an :exc:`ImportError`
+  rather than a :exc:`TypeError` if :func:`__import__` is tried during the
+  Python shutdown process but :data:`sys.path` is already cleared (set to
+  ``None``).
+
 - Issue #21925: :func:`warnings.formatwarning` now catches exceptions when
   calling :func;`linecache.getline` and
   :func:`tracemalloc.get_object_traceback` to be able to log