for i in range(100): print(100 - i)
print [i for i in reversed(range(101))]
You also missed the point of the exercise: start at 0 in your index, but count backward from 100 in output. So the map is 0->100, 1 -> 99, ..., 99 -> 1, 100 -> 0
[1] https://docs.python.org/2/library/functions.html#range