FWIW I tried to backport 825041fc8e2c and test_pyexpat runs without problem.
The snippet of code in msg79398 now raises a ValueError:
>>> from xml.parsers import expat
>>> f=open('/tmp/foo')
>>> p=expat.ParserCreate()
>>> f.close()
>>> p.ParseFile(f)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: I/O operation on closed file