Hashability and dict keys

Question

Accepted Answer

Only hashable objects can be dictionary keys. Tuples are hashable when all their elements are immutable - (1, 2, 3) qualifies. Lists, sets, and dicts are mutable and not hashable. The tricky option is (1, [2, 3]): even though it's a tuple, it contains a mutable list, making the whole tuple unhashable. In interview problems, use tuples to key dictionaries with coordinates or character-count pairs.