Is it a way to know index using itertools.cycle()?

Question

I need to loop trough a list and come back to first element when last item is reached.

The cycle object from itertools is designed for this.

myList = [1,2,3,4,5,6,7,8,9]

i = 0
for item in cycle(myList):
    index = i%9
    print (index)
    i += 1

Is there any other way than using a i variable?

Answer 1

You can use enumerate:

for i, item in enumerate(cycle(myList)):

Below is a demonstration:

>>> from itertools import cycle
>>> for i, item in enumerate(cycle([1, 2, 3])):
...     print i, item
...
0 1
1 2
2 3
3 1
4 2
5 3

You can even give a specific number to start at:

for i, item in enumerate(cycle([1, 2, 3]), 10): # Start at 10

---

Reading @DSM's comment, I realize that you may want to flip the calls to cycle and enumerate:

>>> for i, item in cycle(enumerate([1, 2, 3])):
...     print i, item
...
0 1
1 2
2 3
0 1
1 2
2 3

This will cause i to refer to the index of item in the list rather than act as a counter variable.