I sometimes use your "bug" on purpose in tests, when checking that two values are either both defined or both undefined, but not one defined and one undefined:

$ python

>>> a, b = 1, 2

>>> bool(a) ^ bool(b)

False

>>> a, b = 1, 1

>>> bool(a) ^ bool(b)

False

>>> a, b = None, None

>>> bool(a) ^ bool(b)

False

>>> a, b = None, 1

>>> bool(a) ^ bool(b)

True

(Note: this doesn't work if a value can be 0, because bool(0) is False in Python).

This helps to avoid having to write something like `(a is not None and b is not None) or (a is None and b is None)`.