filter() is also lazy

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Accepted Answer

filter() returns a lazy filter object, not a list. Wrapping it in list() forces evaluation - it iterates the source and keeps only elements where the function returns True. x % 2 == 0 is True for 2 and 4, so the result is [2, 4]. Like map(), filter() is memory-efficient for large iterables because values are produced one at a time.