[issue10794] Infinite recursion while garbage collecting loops indefinitely

[Amaury Forgeot d'Arc]

Amaury Forgeot d'Arc <amauryfa at gmail.com> added the comment:

Normally you should never call __del__, OTOH the issue is the same with a class like::

class A:
    def close(self):
        self.close()
    def __del__(self):
        self.close()

The problem is not with _infinite_ recursion, though; a depth of 47 is enough (but 46 won't show the problem)::

class A:
    def __del__(self):
        self.recurse(47)
    def recurse(self, n):
        if n:
            self.recurse(n-1)
        else:
            raise ValueError

Hint: PyTrash_UNWIND_LEVEL is defined to 50; I checked that recompiling Python with a different value also changes the necessary recursion depth.

There is some nasty interaction between the "Trashcan mechanism" and resurrected objects stored in deep structures. A list is enough, no need to involve frames and exceptions::

class C:
    def __del__(self):
        print ".",
        x = self
        for i in range(49):    # PyTrash_UNWIND_LEVEL-1
            x = [x]
l = [C()]
del l

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nosy: +amaury.forgeotdarc

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<http://bugs.python.org/issue10794>
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