Creating a black and white checkerboard in a two-dimensional array

Question

Is there a better (and shorter) way to create a chessboard, such as an array. Board Requirements:

• Pay
• can be of different sizes (in my example it is 3x3)
• the bottom left square of the board should always be black
• the black square is represented by "B" , the white square is represented by "W"

The code I have is:

 def isEven(number): return number % 2 == 0 board = [["B" for x in range(3)] for x in range(3)] if isEven(len(board)): for rowIndex, row in enumerate(board): if isEven(rowIndex + 1): for squareIndex, square in enumerate(row): if isEven(squareIndex + 1): board[rowIndex][squareIndex] = "W" else: for squareIndex, square in enumerate(row): if not isEven(squareIndex + 1): board[rowIndex][squareIndex] = "W" else: for rowIndex, row in enumerate(board): if not isEven(rowIndex + 1): for squareIndex, square in enumerate(row): if isEven(squareIndex + 1): board[rowIndex][squareIndex] = "W" else: for squareIndex, square in enumerate(row): if not isEven(squareIndex + 1): board[rowIndex][squareIndex] = "W" for row in board: print row 

Output:

 ['B', 'W', 'B'] ['W', 'B', 'W'] ['B', 'W', 'B'] 

Answer 1

What about:

 >>> n = 3 >>> board = [["BW"[(i+j+n%2+1) % 2] for i in range(n)] for j in range(n)] >>> print board [['B', 'W', 'B'], ['W', 'B', 'W'], ['B', 'W', 'B']] >>> n = 4 >>> board = [["BW"[(i+j+n%2+1) % 2] for i in range(n)] for j in range(n)] >>> print board [['W', 'B', 'W', 'B'], ['B', 'W', 'B', 'W'], ['W', 'B', 'W', 'B'], ['B', 'W', 'B', 'W']] 

Answer 2

Kind of hack but

 print [["B" if abs(n - row) % 2 == 0 else "W" for n in xrange(3)] for row in xrange(3)][::-1] 

This is similar to creep requirements or something =)

 def make_board(n): ''' returns an empty list for n <= 0 ''' return [["B" if abs(c - r) % 2 == 0 else "W" for c in xrange(n)] for r in xrange(n)][::-1] 

Answer 3

Here is the itertools solution:

 from itertools import cycle N = 4 colors = cycle(["W","B"]) row_A = [colors.next() for _ in xrange(N)] if not N%2: colors.next() row_B = [colors.next() for _ in xrange(N)] rows = cycle([row_A, row_B]) board = [rows.next() for _ in xrange(N)] 

For N=4 this gives

 ['W', 'B', 'W', 'B'] ['B', 'W', 'B', 'W'] ['W', 'B', 'W', 'B'] ['B', 'W', 'B', 'W'] 

This should be extensible for several colors (for example, the board that goes “B”, “W”, “G”), if you are sure to add each new line and loop to the list of lines.

Answer 4

 for i in range(len(board)): for j in range(len(board)): if isEven(i + j + len(board)): board[i][j] = "W" 

Answer 5

This correctly sets the bottom left corner to "B", always:

 def board(n): def line(n, offset): return [(i+offset) % 2 and 'W' or 'B' for i in range(n)] return [line(n,i) for i in range(n+1,1,-1)] 

Answer 6

It’s cruel to understand. In addition, you can create a rectangular panel:

 def gen_board(width, height): bw = ['B', 'W'] l = [[bw[(j + i) % 2] for j in range(width)] for i in range(height)] # this is done to make sure B is always bottom left # alternatively, you could do the printing in reverse order l.reverse() ## or, we could ensure B is always bottom left by adjusting the index #offset = height%2 + 1 #l = [[bw[(j + i + offset) % 2] for j in range(width)] for i in range(height)] return l def print_board(b): for row in b: print row 

Test Drive:

 >>> print_board(gen_board(4, 3)) ['B', 'W', 'B', 'W'] ['W', 'B', 'W', 'B'] ['B', 'W', 'B', 'W'] 

Answer 7

With single line numpy code without loop:

 import numpy as np chessbool = (np.arange(3)[:, None] + np.arange(3)) % 2 == 0 

and output:

 array([[ True, False, True], [False, True, False], [ True, False, True]] 

To populate an array of W and B :

 chessboard = np.where(chessbool,'B','W') 

and output:

 array([['B', 'W', 'B'], ['W', 'B', 'W'], ['B', 'W', 'B']])