in operator with a nested list

Question

Accepted Answer

The 'in' operator checks whether an item is a direct element of the list, using equality (==). [3, 4] == data[1] is True, so [3, 4] in data is True. But 3 is not a direct element - it lives inside a nested list. To check for membership inside nested structures you'd need to flatten the list or use any(3 in row for row in data).