gh-136047: Allow typing._allow_reckless_class_checks to check _py_abc (#136115)

Author: youknowone

Lib/typing.py

@@ -1866,7 +1866,9 @@ def _allow_reckless_class_checks(depth=2):
     The abc and functools modules indiscriminately call isinstance() and
     issubclass() on the whole MRO of a user class, which may contain protocols.
     """
-    return _caller(depth) in {'abc', 'functools', None}
+    # gh-136047: When `_abc` module is not available, `_py_abc` is required to
+    # allow `_py_abc.ABCMeta` fallback.
+    return _caller(depth) in {'abc', '_py_abc', 'functools', None}
 
 
 _PROTO_ALLOWLIST = {

Misc/NEWS.d/next/Library/2025-07-05-06-59-46.gh-issue-136047.qWvycf.rst

@@ -0,0 +1,2 @@
+Fix issues with :mod:`typing` when the C implementation of :mod:`abc` is not
+available.