Found by Clang trunk's Undefined-Behavior Sanitizer.  [more to come]

Issue #16248: Disable code execution from the user's home directory by tkinter when the -E flag is passed to Python.
Patch by Zachary Ware.

Original patch by Julien Courteau and Pierre Paul Lefebvre.

Issue #16602: When a weakref's target was part of a long deallocation chain, the object could remain reachable through its weakref even though its refcount had dropped to zero.

Thanks to Eugene Toder for diagnosing and reporting the issue.

Patch by Steven Kryskalla.

Thanks to Sean Munkel from docs@

This is necessary for ZFS systems, which don't support UF_IMMUTABLE.
--
Kubilay Kocak (koobs) asked me on IRC to backport this fix to Python 2.7: done!

Patch by Serhiy Storchaka.

Patch by Bruno Dupuis.

The corresponding 3.x commits are 69d5d834c5cb, 40fd26a4206b, and
74d8a2a20c52.

when read several extension modules from the same binary object file.

Patch by Jonathan Kotta.

Patch by Serhiy Storchaka.