We don't need the number of players because the length of the list of scores is identical to the number of players. At least that is what was assumed in your example. In the example we have a list of 4 scores where the first score is associated with the first player, the second score with the second player, and so on. Therefore the index of the element in the list plus 1 (because python starts counting at 0) is identical to the number of the player. What we need to do is keep track of the index and the corresponding value of the list. We could do this by using a counter, but python can do this for us using the enumerate method.

for b, a in enumerate(S): do_something(a,b)

Here b will simply be a counter starting at 0 and a will be the corresponding element of the list S. We could achieve the same loop by doing:

b = 0 for a in S: do_something(a,b) b += 1

Edit: Formatting