Moore neighbourhood in python

Question

I have a grid as a tuple of tuples with integers (1/0), a row number and column number for a cell as integers. And I have to find how many neighbouring cells have neighbours as an integer.

It's a task from the www.checkio.org, an interesting site of learning python.

Here is my code:

def count_neighbours(grid, row, col):
    grid = ()
    count = 0
    for pos in ((row - 1, col), (row + 1, col), (row, col - 1), (row, col + 1), (row - 1, col - 1), (row - 1, col + 1), (row + 1, col - 1), (row + 1, col + 1)):
        if pos == 1:
            count += 1
    return count

The system answers to me that there are no neighbours near the chosen cell. Please explain me what's wrong and thank you for attention!

Answer 1

I see two obvious mistakes:

1. you replaced the grid with an empty tuple

2. your code doesn't reference the grid variable at all, you just add 1 to count if pos is equal to 1. pos will never be equal to 1, because you are setting it to one of a series of tuples.

Ergo, your function will always return 0 as long as row and col are numeric (and raises an exception otherwise).

You need to actually reference the grid that is passed in:

def count_neighbours(grid, row, col):
    count = 0
    for pos in (
            (row - 1, col), (row + 1, col), (row, col - 1),
            (row, col + 1), (row - 1, col - 1), (row - 1, col + 1),
            (row + 1, col - 1), (row + 1, col + 1)):
        if grid[pos[0]][pos[y]] == 1:
            count += 1
    return count

I'm assuming here that the grid is a list of lists representing rows and cells.

Next, you'll have to handle your positions going out of bounds; there are no neighbours to the top of the first row, for example:

def count_neighbours(grid, row, col):
    count = 0
    for x, y in (
            (row - 1, col), (row + 1, col), (row, col - 1),
            (row, col + 1), (row - 1, col - 1), (row - 1, col + 1),
            (row + 1, col - 1), (row + 1, col + 1)):
        if not (0 <= x < len(grid) and 0 <= y < len(grid[x])):
            # out of bounds
            continue
        if grid[x][y] == 1:
            count += 1
    return count