Now, when compare errors raised during `in`, dict.keys(), dict.values() and set all propagate the errors. But dict.items() will swallow the errors(only key compare): >>> class BadEq: ... def __hash__(self): ... return 7 ... def __eq__(self, other): ... raise RuntimeError ... >>> k1, k2, v1, v2 = BadEq(), BadEq(), BadEq(), BadEq() >>> d = {k1: v1} >>> k2 in d.keys() Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 5, in __eq__ RuntimeError >>> v2 in d.values() Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 5, in __eq__ RuntimeError >>> k2 in {k1} Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 5, in __eq__ RuntimeError >>> (k2, v2) in d.items() False >>> (k2, v1) in d.items() False dictitems_contains.patch tries to fix this.

New changeset 2a9e0e869ca7 by Raymond Hettinger in branch '3.5': Issue #28189: dictitems_contains no longer swallows compare errors. https://hg.python.org/cpython/rev/2a9e0e869ca7

Thanks for the patch.

Thanks for the merge Raymond. :)