- iterator를 상속받음
- (index, value)
a = enumerate([1,2,3])
a
==> <enumerate at 0x7f92fdd4cd70>
next(a)
==> (0, 1)
next(a)
==> (1, 2)
next(a)
==> (2, 3)
next(a)
==> StopIteration:
from collections import Iterator #Iterator로 부터 상속 받음
issubclass(enumerate, Iterator)
==> True