Question

I am using Python to write a program that looks through lists of lists and changes values.

In my list of lists I have 3’s and I want to find their index. Right now I can only get it to work on the first row. I want it to find 3’s on any of the lists in “numbers.”

Here is some sample code to wash away the mud:

numbers = [
    [3, 3, 3, 5, 3, 3, 3, 3, 6],
    [8, 0, 0, 0, 4, 7, 5, 0, 3],
    [0, 5, 0, 0, 0, 3, 0, 0, 0],
    [0, 7, 0, 8, 0, 0, 0, 0, 9],
    [0, 0, 0, 0, 1, 0, 0, 0, 0],
    [9, 0, 0, 0, 0, 4, 0, 2, 0],
    [0, 0, 0, 9, 0, 0, 0, 1, 0],
    [7, 0, 8, 3, 2, 0, 0, 0, 5],
    [3, 0, 0, 0, 0, 8, 0, 0, 0],
    ]
a = -1
while a:
    try:
        for row in numbers:
            a = row[a+1:].index(3) + a + 1
            print("Found 3 at index", a)
    except ValueError:
        break

When I run it I get:

Found 3 at index 0
Found 3 at index 1
Found 3 at index 2
Found 3 at index 4
Found 3 at index 5
Found 3 at index 6
Found 3 at index 8

Which shows that it is working but only on the first row.

Thanks!

Answer 1

Here’s a little code snippet to get you started:

>>> for i, row in enumerate(numbers):
        if 3 in row:
            print i, row.index(3)   

1 8
2 5
7 3
8 0

>>> numbers[1][8]
3
>>> numbers[2][5]
3
>>> numbers[7][3]
3
>>> numbers[8][0]
3