Issue #16824: Fix a failure guard in the never reached in the normal test execution code in test_pep380.

because it evaluates its condition before pyET is even set by test_main.
Therefore, the check it moved to "runtime".

it properly to avoid problems with test-run-order dependencies.

Patch by Matthew Barnett.

Issue #16485: Fix file descriptor not being closed if file header patching fails on closing of aifc file.

Issue #16485: Fix file descriptor not being closed if file header patching fails on closing of aifc file.

other threads.

The code isn't exactly equivalent because a classmethod would
only make sense inside a chain class, and it would need "cls"
as a first argument, and it would need to return an instance
of "chain" rather than a generator.

The updated example drops the @classmethod decorator so that
it can be used standalone:  list(from_iterable(['abc', 'def']))
This should be communicate what from_iterable does.