IndexError list index out of range

hey,

i’ve got an error with my code which i cant figure out im new to python!
This is my code.

def winner(grid):
    for across in range(4):
        row = across * 4
        line = grid[row] + grid[row+10] + grid[row+20] + grid[row+30]
        if line == "XXXX" or line == "OOOO":
            return True

    for down in range(4):
        line = grid[down] + grid[down+40] + grid[down+80] + grid[down+12]
        if line == "XXXX" or line == "OOOO":
            return True

    line = grid[00] + grid[50] + grid[10] + grid[15]
    if line == "XXXX" or line == "OOOO":
            return True

    line = grid[30] + grid[60] + grid[90] + grid[12]
    if line == "XXXX" or line == "OOOO":
            return True

This is the area of the code which has an error but i dont understand it.

IndexError: list index out of range

Please help!

Thanks in advance

It should be pretty easy to figure out what that error message means by googling. It’s already fairly plainly worded though.