Reversi text board parsing to bitfield

Question

This Python code parses string representations of Reversi boards and converts them into bit string suitable for use by a bitstring module: b = BitArray('0b110') or bitarray module: a = bitarray('000111') if blackInit and whiteInit are initialized as empty strings.

I am interested in a simpler way to do this in Python. I would like to preserve the idea of having a human readable string representation of the board converted into 2 bitstrings, one for the black pieces and one for the white pieces. It seems like it could be simpler if it was just a split and then a map instead of a loop, but I wanted to be able to see the strings line by line and don't see how to workaround that.

board1 = [
        '_|_|_|_|_|_|_|_',
        '_|_|_|_|_|_|_|_',
        '_|_|_|_|_|_|_|_',
        '_|_|_|_|_|_|_|_',
        '_|_|_|_|_|_|_|_',
        '_|_|_|_|_|_|_|_',
        '_|_|_|_|_|_|_|_',
        '_|_|_|_|_|_|_|_']

board2 = [
        'B|_|_|_|_|_|_|W',
        '_|_|_|_|_|_|_|_',
        '_|_|_|_|_|_|_|_',
        '_|_|_|_|_|_|_|_',
        '_|_|_|_|_|_|_|_',
        '_|_|_|_|_|_|_|_',
        '_|_|_|_|_|_|_|_',
        'W|_|_|_|_|_|_|B']

board3 = [
        'W|W|W|W|B|B|B|B',
        'W|_|_|_|_|_|_|B',
        'W|_|_|_|_|_|_|B',
        'W|_|_|_|_|_|_|B',
        'B|_|_|_|_|_|_|W',
        'B|_|_|_|_|_|_|W',
        'B|_|_|_|_|_|_|W',
        'B|B|B|B|W|W|W|W']

board4 = [
        '_|_|_|_|_|_|_|_',
        '_|_|_|_|_|_|_|_',
        '_|_|_|_|_|_|_|_',
        '_|_|_|W|B|_|_|_',
        '_|_|_|B|W|_|_|_',
        '_|_|_|_|_|_|_|_',
        '_|_|_|_|_|_|_|_',
        '_|_|_|_|_|_|_|_']

board5 = [
        'W|_|_|_|_|_|_|B',
        '_|W|_|_|_|_|B|_',
        '_|_|W|_|_|B|_|_',
        '_|_|_|W|B|_|_|_',
        '_|_|_|B|W|_|_|_',
        '_|_|B|_|_|W|_|_',
        '_|B|_|_|_|_|W|_',
        'B|_|_|_|_|_|_|W']


def parse_board(board):
    def map_black(spot):
         return str(int(spot == 'B'))
    def map_white(spot):
         return str(int(spot == 'W'))
    blackInit = '0b'
    whiteInit = '0b'
    for line in board:
        squares = line.split('|')
        blackInit = blackInit + ''.join(map(map_black,squares))
        whiteInit = whiteInit + ''.join(map(map_white,squares))
    return (blackInit,whiteInit)

print(parse_board(board1))
print(parse_board(board2))
print(parse_board(board3))
print(parse_board(board4))
print(parse_board(board5))

Answer 1

def parse_board(board):
    def map_black(spot):

This name suggests that the function is a variant on map. Whereas its actually intended to be used as a parameter on map

         return str(int(spot == 'B'))
    def map_white(spot):
         return str(int(spot == 'W'))

Both functions are very similiar, can you refactor?

    blackInit = '0b'
    whiteInit = '0b'

The python style guide suggest 'lowercase_with_underscores' for local variable names

    for line in board:
        squares = line.split('|')
        blackInit = blackInit + ''.join(map(map_black,squares))
        whiteInit = whiteInit + ''.join(map(map_white,squares))

Repeatedly adding strings is not very efficient python.

    return (blackInit,whiteInit)

Everything in your function is done twice. Once for 'B' and once for 'W'. I'd suggest you should have a function that takes 'B' or 'W' as parameter, and call that twice.

Here's how I'd tackle this:

def bitstring_from_board(board, letter):
    bits = []
    for line in board:
        bits.extend( spot == letter for spot in line.split('|') )
    return '0b' + ''.join(str(int(x)) for x in bits)

def parse_board(board):
    return bitstring_from_board(board, 'B'), bitstring_from_board(board, 'W')