Test your knowledge: Python map and filter

Review

1. What does map double when given [1, 2, 3] produce when fully iterated, if double(x) returns x * 2?

   map yields the function result for each input item.
2. When filter(is_even, [1, 2, 3, 4]) is iterated, what values remain?

   filter keeps the original items for which the test is true.
3. What does filter(None, [0, "ok", "", 3]) keep?

   Falsey items are removed and truthy original items remain.
4. Why does a second list(result) call on the same map result produce an empty list after the first call consumes it?

   map returns an iterator, and an iterator is exhausted by iteration.
5. With map(add, [1, 2], [10, 20, 30]), how many results are produced by default?

   map uses one item from each iterable at a time and stops when the shortest iterable is exhausted.