IndexError: list index out of range for nested list

Question

I have a list that contains lists of 5 values and i'm getting an index out of range error when trying to run a while loop if a value in the list is == 5. Here is pretty much all my code

from solverFuncs import *
puzzle = [[0,0,0,0,0],[0,0,0,0,0],[0,0,0,0,0],[0,0,0,0,0],[0,0,0,0,0]]

pos = 0
backtrack = 0
checks = 0

while pos <25:
    puzzle[pos/5][pos%5] += 1
    checks+=1
    if check_valid(puzzle,cages):
        pos+=1
    elif puzzle[pos/5][pos%5]==5:
        while puzzle[pos/5][pos%5]==5:
            puzzle[pos/5][pos%5]=0
            pos=pos-1
            backtrack+=1

The error im getting shows up as such:

File "solver.py", line 16, in <module>
while puzzle[pos/5][pos%5]==5:
IndexError: list index out of range

Answer 1

In python, list's indexes starts with [0]. So you have 5 elements in your list with min index = 0 and max index = 4 . Hope it will help

Answer 2

Whatever check_valid does, I think you should add a check in the while block at line 16

while pos>=0 and puzzle[pos/5][pos%5]==5:

and also adding pos=0 before going back to while pos<25