On Wed, Jun 11, 2014, at 17:11, Nikolaus Rath wrote: > MRAB <pyt...@mrabarnett.plus.com> writes: > > On 2014-06-11 02:30, Nikolaus Rath wrote: > >> Hello, > >> > >> I recently noticed (after some rather protacted debugging) that the > >> io.IOBase class comes with a destructor that calls self.close(): > >> > >> [0] nikratio@vostro:~/tmp$ cat test.py > >> import io > >> class Foo(io.IOBase): > >> def close(self): > >> print('close called') > >> r = Foo() > >> del r > >> [0] nikratio@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? > >> > > To me, it makes sense. You want to make sure that it's closed, releasing > > any resources it might be holding, even if you haven't done so > > explicitly. > > I agree with your intentions, but I come to the opposite conclusion: > automatically calling close() in the destructor will hide that there's a > problem in the code. Without that automatic cleanup, there's at least a > good chance that a ResourceWarning will be emitted so the problem gets > noticed. "Silently work around bugs in caller's code" doesn't seem like > a very useful default to me...
Things which actually hold system resources (like FileIO) give ResourceWarning if they close in __del__, so I don't understand your point. _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com