On Thu, Jun 12, 2014, at 18:06, Nikolaus Rath wrote:
> Consider this simple example:
>
> $ cat test.py
> import io
> import warnings
>
> class StridedStream(io.IOBase):
> def __init__(self, name, stride=2):
> super().__init__()
> self.fh = open(name, 'rb')
> self.stride = stride
>
> def read(self, len_):
> return self.fh.read(self.stride*len_)[::self.stride]
>
> def close(self):
> self.fh.close()
>
> class FixedStridedStream(StridedStream):
> def __del__(self):
> # Prevent IOBase.__del__ frombeing called.
> pass
>
> warnings.resetwarnings()
> warnings.simplefilter('error')
>
> print('Creating & loosing StridedStream..')
> r = StridedStream('/dev/zero')
> del r
>
> print('Creating & loosing FixedStridedStream..')
> r = FixedStridedStream('/dev/zero')
> del r
>
> $ python3 test.py
> Creating & loosing StridedStream..
> Creating & loosing FixedStridedStream..
> Exception ignored in: <_io.FileIO name='/dev/zero' mode='rb'>
> ResourceWarning: unclosed file <_io.BufferedReader name='/dev/zero'>
>
> In the first case, the destructor inherited from IOBase actually
> prevents the ResourceWarning from being emitted.
Ah, I see. I don't see any good ways to fix it, though, besides setting
some flag if close() is called from __del__.
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