(Based on patch by Serhiy Storchaka.)

(Based on patch by Serhiy Storchaka.)

implementation in issue #21408 they are redundant.

collections module now accept the self keyword argument.

This gives an earlier and more visible failure if a link is deleted
during iteration.

reverse iteration using reversed().

ModuleNotFoundError.

Use the cleaner looking @property style for __dict__.
Move _replace() to be just after make() to indicate that
it is a core method on named tuples.

size and pickling time.

Backed out changeset c4ca39bece9d

weakref callbacks.

This is 2e446e87ac5b except that collections/__init__.py has been
modified to import proxy from _weakref instead of weakref.  This
eliminates an import cycle which seems to cause a problem on Unix but
not Windows.