[Python-Dev] Why does IOBase.del call .close? (original) (raw)
Nikolaus Rath Nikolaus at rath.org
Wed Jun 11 03:30:49 CEST 2014
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Hello,
I recently noticed (after some rather protacted debugging) that the io.IOBase class comes with a destructor that calls self.close():
[0] nikratio at vostro:/tmp$ cat test.py
import io
class Foo(io.IOBase):
def close(self):
print('close called')
r = Foo()
del r
[0] nikratio at vostro:/tmp$ python3 test.py
close called
To me, this came as quite a surprise, and the best "documentation" of this feature seems to be the following note (from the io library reference):
"The abstract base classes also provide default implementations of some methods in order to help implementation of concrete stream classes. For example, BufferedIOBase provides unoptimized implementations of readinto() and readline()."
For me, having del call close() does not qualify as a reasonable default implementation unless close() is required to be idempotent (which one could deduce from the documentation if one tries to, but it's far from clear).
Is this behavior an accident, or was that a deliberate decision?
Best, -Nikolaus
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