How to start from second index for for-loop

Question

I have this for-loop. I want i in range(nI) to start from the second number in the I list. Could you guide me?

I=[0,1,2,3,4,5,6]
nI=len(I)
for i in range(nI):
    sum=0
    for v in range(nV):
        for j in range(nJ):
            sum=sum+x1[i][j][v]
return sum

Answer 1

If you want to iterate through a list from a second item, just use range(1, nI) (if nI is the length of the list or so).

for i in range(1, nI):
    sum=0
    for v in range(nV):
        for j in range(nJ):
            sum=sum+x1[i][j][v]

Probaly, a part of your function just lost somewhere, but anyway, in in general range() works like this:

range(start_from, stop_at, step_size)

i. e.

for i in range(2, 7, 2):
    print(i, end=' ')

Out:
2 4 6

Edit

Please, remember: python uses zero indexing, i.e. first element has an index 0, the second - 1 etc.

By default, range starts from 0 and stops at the value of the passed parameter minus one. If there's an explicit start, iteration starts from it's value. If there's a step, it continues while range returns values lesser than stop value.

for i in range(1, 7, 2):
    print(i, end=' ')

Out: 
1 3 5  # there's no 7!

Detailed description of range build-in is here.