Taking slice of an iterator

>>> def count(n):
...     while True:
...             yield n
...             n += 1
...
>>> c = count(0)
>>> c[10:20]
Traceback (most recent call last):
  File "", line 1, in
TypeError: 'generator' object has no attribute '__getitem__'>>> for x in itertools.islice(c, 10, 20):
...     print x
...
10
11
12
13
14
15
16
17
18
19

islice() will consume data on the iterator. Iterators can't be rewound. If it needs go back, just turn the data into a list first.

>>> next(c)
20
>>> next(c)
21
>>> for x in itertools.islice(c, 10, 20):
...     print x
...
32
33
34
35
36
37
38
39
40
41