grid.py

grid = [
    [" ", " ", " "],
    [" ", " ", " "],
    [" ", " ", " "]]

def is_winner(player):
    return (
        # Rows
        grid[0][0] == player and grid[0][1] == player and grid[0][2] == player or
        grid[1][0] == player and grid[1][1] == player and grid[1][2] == player or
        grid[1][0] == player and grid[1][1] == player and grid[1][2] == player or
        # Columns
        grid[0][0] == player and grid[1][0] == player and grid[2][0] == player or
        grid[0][1] == player and grid[1][1] == player and grid[2][1] == player or
        grid[0][2] == player and grid[1][2] == player and grid[2][2] == player or
        # Diagonals
        grid[0][0] == player and grid[1][1] == player and grid[2][2] == player or
        grid[0][2] == player and grid[1][1] == player and grid[2][0] == player)