On Wed, Oct 14, 2009 at 3:16 PM, Neil Schemenauer <nas@arctrix.com> wrote:
The current shutdown code in pythonrun.c zaps module globals by
setting them to None (an attempt to break reference cycles). That
causes problems since __del__ methods can try to use the globals
after they have been set to None.

The procedure implemented by http://bugs.python.org/issue812369
seems to be a better idea. References to modules are replaced by
weak references and the GC is allowed to cleanup reference cycles.

Based on the description, it still resorts to zapping module globals by setting them to None.  It zaps them to weakrefs first, which means that globals are more likely to be valid during __del__, but it still cannot make any guarantees and referencing globals from __del__ is still a bad idea.  Is that a correct synopsis?
Daniel Stutzbach, Ph.D.
President, Stutzbach Enterprises, LLC