gh-130094: Fix race condition in _find_spec

Entries may be added or removed from `sys.meta_path` concurrently. For
example, setuptools temporarily adds and removes the `distutils`
finder from the beginning of the list. The local copy ensures that we
don't skip over any entries.

Author: colesbury

Lib/importlib/_bootstrap.py

@@ -1244,6 +1244,9 @@ def _find_spec(name, path, target=None):
         raise ImportError("sys.meta_path is None, Python is likely "
                           "shutting down")
 
+    # gh-130094: copy sys.meta_path so that we have a consistent view of the
+    # list while iterating over it.
+    meta_path = list(meta_path)
     if not meta_path:
         _warnings.warn('sys.meta_path is empty', ImportWarning)
 

Misc/NEWS.d/next/Core_and_Builtins/2025-02-14-00-32-52.gh-issue-130094.m3EF9E.rst

@@ -0,0 +1 @@
+TODO