The io documentation says:

IOBase is also a context manager and therefore supports the with statement. In this example, file is closed after the with statement’s suite is finished—even if an exception occurs:

with open('spam.txt', 'w') as file:
    file.write('Spam and eggs!')


I read this to mean that my own subclass of io.BufferedIOBase would call close() when used as a context manager.

Instead, it is necessary to provide an implementation of __exit__ that calls close() to get this behavior.

The documentation lists Mixin Methods, but I couldn't find a definition of the term "Mixin Methods" in the docs.

Please post or attach *minimal* and complete (runnable as is) code that does not do what you expect.

I cannot reproduce the issue. __exit__() calls close().

>>> import io
>>> class F(io.IOBase):
...     def close(self):
...         print('close')
...         super().close()  # set closed = True
... 
>>> with F(): pass
... 
close

Thanks, I'm sorry I didn't save when I was having my strange problem.

The io module is still practically undocumented. It should have examples subclasses for each class, perhaps a link to the PEP and a link to a Python implementation of the module.

Possibly the best io module example I've found https://github.com/python/cpython/blob/master/Lib/_compression.py