Why is this for loop starting at index 1 instead of index 0?

I am trying to get a better understanding of a nested for loop in python:

nums = [2,4,6,8,10]

for i in range(len(nums)):
    for j in range(i):
        print("i: " + str(i))
        print("j: " + str(j))

i is starting at index 1 instead of index 0, but if I change the range of for j in range(i) to anything other than the variable i, it starts at index 0.

If someone could quickly explain the functionality of this, it would be greatly appreciated.

Answer

When i=0, range(i) is empty, so it skips the inner loop:

>>> list(range(0))
[]