>>> import io
>>> class MyIO(io.FileIO):
...     def flush(self):
...             print('closed:', self.closed)
...
>>> f = MyIO('test.out', 'wb')
>>> f.close()
closed: True

IMHO, calling flush() after the file has already been closed is
incorrect behaviour. Search for "Possible py3k io wierdness" on
python-dev for discussion.