[Python-Dev] Why does IOBase.del call .close? (original) (raw)
Benjamin Peterson benjamin at python.org
Fri Jun 13 07:27:49 CEST 2014
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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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