象棋的主教运动

Question

I'm doing a chess game for a school project in python3. I'm stuck at the bishop movement. I did everything move for all the pieces but the bishop is really hard. Here is how I code my board:

board=[["R1W","C1W","F1W","K1W","D1W","F2W","C2W","R2W"],
       ["P1W","P2W","P3W","P4W","P5W","P6W","P7W","P8W"],
       ["___","___","___","___","___","___","___","___"],
       ["___","___","___","___","___","___","___","___"],
       ["___","___","___","___","___","___","___","___"],
       ["___","___","___","___","___","___","___","___"],
       ["P1N","P2N","P3N","P4N","P5N","P6N","P7N","P8N"],
       ["R1N","C1N","F1N","D1N","K1N","F2N","C2N","R2N"]]

and here is how I program my bishop:

def fou_valide(piece,l,m,c,n):
    if piece[0]=="F":
        if (abs(m-l)+abs(n-c))%2==0 and l!=m and  n!=c and board_fou_dame[l][c]==board_fou_dame[m][n] and abs(l-m)==abs(c-n):
            if m>l and n>c:
                for x in range(l+1,m):# on scanne les cases ou va passer la piece si elle ne passe par-dessus une pieces en effet elle ne peut pas sauter au dessus d\'une autre piece
                    for y in range(c+1,n):
                        if board[x][y]!="___":
                            print ("faux")
                            return False
                return True
            elif m>l and n<c:
                for z in range(l+1,m):# on scanne les cases ou va passer la piece si elle ne passe par-dessus une pieces en effet elle ne peut pas sauter au dessus d\'une autre piece
                    for j in range(c-1,n,-1):
                        if board[z][j]!="___":
                            print ("fau")
                            return False

That's just half the code only l , m , n , and c are changing. My problem is that even though n>c , it shows "fau" instead of "faux"

Here is how I ask for position:

l = int(input("ligne de selection?:\n"))-1 #on demande au joueur la ligne de la piece a selectionné
c = int(input("colonne de selection?:\n"))-1#on demande au joueur la colonne de la piece a selectionné
m = int(input("ligne de destination ?:\n"))-1#on demande au joueur la ligne ou il veut pose la piece
n = int(input("colonne de destination?:\n"))-1#on demande au joueur la colonne ou il veut pose la piece
piece = board[l][c] # piece correspond a la piece selectionné

Answer 1

In fact, piece is useles since you have l and c .
In your function, you have to verify four things.

1) that the piece is indeed a bishop
2) that l and c are differnt from m and c
3) that they are on the same diagonal
4) that the cells between the two are free

The 4) is the hardest unless you remark that the direction you need to check is (sign(m - l), sign(n - c)) . There's no need to write a different piece of code for each direction or each color.

EDIT: There's no built-in sign function, you need to write it yourself.

def sign(n):
    return 1 if n >= 0 else -1

Then, you can check the cells with a single while loop that works for any direction.

def can_eat(l, c, m, n):
    dl = sign(m - l)
    dc = sign(n - c)
    x, y = c + dc, l + dl
    while x != n and y != m:
        if board[y][x] != '___': # non empty cell
            return False
        x += dc
        y += dl
    return True

Answer 2

So thanks to Bruno L, it now works fine, here is the code for the bishop that i used, this is a simplified version :

def fou_valide(piece,l,m,c,n,):
if piece[0]=="F":#F in french stand for bishop, "Fou", 
    if l!=m and  n!=c  and abs(l-m)==abs(c-n): #the condition for the bishop movement
        dl = sign(m - l)#it get the me direction of the movement
        dc = sign(n - c)
        x, y = c + dc, l + dl
        while x != n and y != m:#This check if they are any non-empty cell on the way
            if board[y][x] != '___': # non empty cell
                return False
            x += dc
            y += dl
        return True
    return False
return True

Here is the sign function:

def sign(z):
if z >= 0:
    return 1  
else:
    return -1