Annoying Python list index out of range error

Question

I have an array already initialized to be a 3x6 array called self.ascii. I am trying alter a 3x3 block of this array at a time, using the code:

for x in range(3):
    for y in range(3):
       # currY and currX represent the bottom left corner of the 3x3 square I am tyring to alter
       self.ascii[y+currY][x+currX] = arr[y][x] # yes I know the x and y values are backwards between the arrays

However I keep getting the error, in GNURadio-Companion list index out of range--before I even try to run it. I know that the indexes here do not leave the range of the list.

Question: Why does python check this before running, and is there a different way I should be loading these 3x3 arrays

Can you post the traceback message that shows the failing line? Python doesn't check list indexes before you run it, so something else is going on. Printing `self.ascii`, plus `currY` and `currX` would be useful. One of these is different than you think. — tdelaney, Apr 10 '20 at 03:40
If `currY` is bottom left, then the rows you want are `currY-0`, `currY-1` and `currY-2`, but you are adding postive numbers here. Perhaps you want `self.ascii[currY-y][currX+x]` or maybe since you use y on both sides, `self.ascii[currY-3+y]` — tdelaney, Apr 10 '20 at 03:54

score 1 · Answer 1 · answered Apr 10 '20 at 03:38

Learn to use pdb.

import pdb

pdb.set_trace()

# Now your code.
for x in range(3):
    for y in range(3):
       self.ascii[y+currY][x+currX] = arr[y][x]

This will drop you into an interpreter where you can see the value of anything you like, and use commands like n to execute the next instruction in the code. Go step by step until you find which index is going outside the range of its list.

Annoying Python list index out of range error

1 Answers1