[issue38525] Strange reversed dict behavior

[Serhiy Storchaka]

Serhiy Storchaka <storchaka+cpython at gmail.com> added the comment:

The proposed fix fixes a crash, but there is other bug in iterating shared dicts.

class A:
    def __init__(self, x, y):
        if x: self.x = x
        if y: self.y = y

a = A(1, 2)
print(list(iter(a.__dict__)))
print(list(reversed(a.__dict__)))
b = A(1, 0)
print(list(iter(b.__dict__)))
print(list(reversed(b.__dict__)))

With PR 16846 the last print outputs [] instead of expected ['x']. It crashes without PR 16846, so this issue is not only about empty dicts.

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nosy: +serhiy.storchaka

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue38525>
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