Why list() with an object shows different results respectively?

Question

The outcome is None with list(a) the second time. Anyone have a clue on that?

>>> test = {1: 2, 3: 4}
>>> a= test.iterkeys()
>>> list(a)
**[1, 3]**
>>> list(a)
**[]**
>>> list(a)
[]

its an iterable, once you consume the values they are gone. – gold_cy May 30 '17 at 19:17 — gold_cy, May 30 '17 at 19:17
Because `.iterkeys` returns a single pass iterator. – juanpa.arrivillaga May 30 '17 at 19:18 — juanpa.arrivillaga, May 30 '17 at 19:18

score 7 · Answer 1 · answered May 30 '17 at 19:18

7

iterkeys returns an iterator, which, as any iterator, can be iterated over only once.

list consumes the whole iterator, so that the latter can't provide any more values, so the subsequent lists are empty.

answered May 30 '17 at 19:18

ForceBru

1 Answers1