Python Connect four Diagonal Checking

Question

I'm having issue getting my code started. I have a Connect 4 project for my programming class and I'm having a really stupid issue. I don't understand the diagonal checking. He gave us an example but I honestly don't get it.

def CheckForWinner(board, playerName, playerChar):


diagonal = board[2][0] + board[3][1] + board[4][2] + board[5][3]
if playerChar * 4 in diagonal:
    return playerName

It is a 42 space board(7x6)

 1 2 3 4 5 6 7 
 _ _ _ _ _ _ _ 
|_|_|_|_|_|_|_|
|_|_|_|_|_|_|_|
|_|_|_|_|_|_|_|
|_|_|_|_|_|_|_|
|_|_|_|_|_|_|_|
|_|_|_|_|_|_|_|

I'm just having difficulties under standing what it is checking. I'm not asking for you to give me the code. Just an explanation please. :)

Answer 1

It's building a string up of the characters stored in a diagonal. For example, if the board is:

 1 2 3 4 5 6 7 
 _ _ _ _ _ _ _ 
|_|A|_|_|_|_|_|
|_|_|B|_|_|_|_|
|_|_|_|C|_|_|_|
|_|_|_|_|D|_|_|
|_|_|_|_|_|_|_|
|_|_|_|_|_|_|_|

Then the following line:

diagonal = board[2][0] + board[3][1] + board[4][2] + board[5][3]

will assign the value ABCD to the variable diagonal , because it's concatenating the characters in board[2][0] ( A ), board[3][1] ( B ), etc... into one string: ABCD .

The if statement makes up a 4-character string of the player's character, and checks if it is in the diagonal string. If the player's character is X , for example, then the if evaluates to checking if XXXX is in ABCD . It will then return the player's name if this is True , which means they've won.

(Of course, the actual location of the A, B, C and D in my example depends on what way round the list of lists is representing the board)

Answer 2

1 2 3 4 5 6 7 
 _ _ _ _ _ _ _ 
|_|_|_|_|_|_|_|
|_|_|_|_|_|_|_|
|_|_|_|_|W|_|_|
|_|_|_|Z|_|_|_|
|_|_|Y|_|_|_|_|
|_|X|_|_|_|_|_|

x = 2,0
y = 3,1
z = 4,2
w = 5,3

it is probably using 1 for player 1 and 2 for player 2 so the board would look like this as an array (note that the array is probably (row) inverted from the displayed grid.)

player = 2
the_board = [[0,0,2,0,0,0,0],  
             [0,0,0,2,0,0,0],
             [0,0,0,0,2,0,0],
             [0,0,0,0,0,2,0],
             [0,0,0,0,0,0,0],
             [0,0,0,0,0,0,0]]
print the_board[2][0]  #2
diagonal = the_board[2][0] + the_board[3][1] + the_board[4][2] + the_board[5][3] # 2+2+2+2 = 8
player * 4  == diagonal # 2*4 =?= 2+2+2+2