is vs ==

Question

is vs ==

Accepted Answer

a == b calls a.__eq__(b) and asks whether the two objects represent the same value. a is b compares their id() - it returns True only if they are literally the same object in memory. The practical rule: use == for value comparisons, and reserve is for checking against singletons like None, True, and False. Writing x == None works but is considered bad style because a custom class could define __eq__ to return True unexpectedly; x is None is always correct.