[issue27275] KeyError thrown by optimised collections.OrderedDict.popitem()

[Dennis Sweeney]

Dennis Sweeney <sweeney.dennis650 at gmail.com> added the comment:

bpo-44782 was opened about the `class LRU(OrderedDict)` in the OrderedDict docs, and its pop() method failing.

I think Serhiy's patch here (before revert) may be a good idea (to re-apply).
I think it is reasonable to ignore user-implemented dunder methods from subclasses.
Concrete type implementations generally do not behave as mix-ins:

    def never_called(self, *args):
        print("Never called.")
        raise ZeroDivisionError

    class MyList(list):
        __setitem__ = __delitem__ = __getitem__ = __len__ = __iter__ = __contains__ = never_called

    class MyDict(dict):
        __setitem__ = __delitem__ = __getitem__ = __len__ = __iter__ = __contains__ = never_called

    class MySet(set):
        __setitem__ = __delitem__ = __getitem__ = __len__ = __iter__ = __contains__ = never_called

    L = MyList([5, 4, 3, 2])
    L.sort()
    L.pop(1)
    L.insert(0, 42)
    L.pop()
    L.reverse()
    assert type(L) is MyList

    D = MyDict({"a": 1, "b": 2, "c": 3})
    assert D.get(0) is None
    assert D.get("a") == 1
    assert D.pop("b") == 2
    assert D.popitem() == ("c", 3)
    assert type(D) is MyDict

    S = MySet({"a", "b", "c"})
    S.discard("a")
    S.remove("b")
    S.isdisjoint(S)
    S |= S
    S &= S
    S ^= S
    assert type(S) is MySet

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nosy: +Dennis Sweeney

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<https://bugs.python.org/issue27275>
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