Shorten down ifs for grid checking

I’m in the making of a 4-in-a-Row game with a grid system. Was thinking of shortening it down with a for loop, but it ended up making the player randomly win. Any tips is appreciated.

if grid[4][row] == '.':
    grid[4][row] = 'X'
else:
    if grid[3][row] == '.':
        grid[3][row] = 'X'
    else:
        if grid[2][row] == '.':
            grid[2][row] = 'X'
        else:
            if grid[1][row] == '.':
                grid[1][row] = 'X'
            else: 
                if grid[0][row] == '.':
                    grid[0][row] = 'X'

>Solution :

Right off the bat, you can use elif:

if grid[4][row] == '.':
    grid[4][row] = 'X'
elif grid[3][row] == '.':
    grid[3][row] = 'X'
elif grid[2][row] == '.':
    grid[2][row] = 'X'
elif grid[1][row] == '.':
    grid[1][row] = 'X'
elif grid[0][row] == '.':
    grid[0][row] = 'X'

You can then replace this with a simple loop which will exit early if it finds a .:

for n in range(4, -1, -1):
    if grid[n][row] == '.':
        grid[n][row] = 'X'
        break

If grid is a list, you can use a reversed slice instead of iterating over specific indices.

for c in grid[4::-1]:
    if c[row] == '.':
        c[row] = 'X'
        break

If you want to get fancier, use any with an assignment expression:

if any((c:=grid[n])[row] == '.' for n in range(4, -1, -1)):
    c[row] = 'X'

# Or for a list,
# if any((c:=x)[row] == '.' for x in grid[4::-1]):
#     c[row] = 'X'

As soon as any sees a value of n (or x) that makes the expression true, it returns True, and the name c remains bound to the element of grid that made the expression true.