Movatterモバイル変換
[0]ホーム
[Python-Dev] Why does IOBase.__del__ call .close?
Nikolaus RathNikolaus at rath.org
Thu Jun 12 02:11:53 CEST 2014
MRAB <python at 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 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?>>> 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 aproblem in the code. Without that automatic cleanup, there's at least agood chance that a ResourceWarning will be emitted so the problem getsnoticed. "Silently work around bugs in caller's code" doesn't seem likea very useful default to me...Best,-Nikolaus-- GPG encrypted emails preferred. Key id: 0xD113FCAC3C4E599FFingerprint: ED31 791B 2C5C 1613 AF38 8B8A D113 FCAC 3C4E 599F »Time flies like an arrow, fruit flies like a Banana.«
More information about the Python-Devmailing list
[8]ページ先頭