Reads go sgf file from stdin and returns 180 degrees rotated on stdout

flip_go_board.py

import re
import string
import sys


class Flipper(object):
    flip_re = re.compile('\[([a-z]{2})\]')

    def __init__(self, board_size=19):
        self.board_size = board_size
        self.scale = string.ascii_lowercase[:board_size]

    def flip_coordinates(self, match):
        coordinates = match.group(1)
        s = self.scale
        b = self.board_size
        return '[' + ''.join([s[b-s.index(c)-1] for c in coordinates]) + ']'

    def flip_sgf(self, iterable):
        return [self.flip_re.sub(self.flip_coordinates, l) for l in iterable]


if __name__ == '__main__':
    flipper = Flipper()
    for line in flipper.flip_sgf(sys.stdin):
        sys.stdout.write(line)

However after I've realized that sgf does not avoid i/j ambiguity, all this snippet almost lost it's purpose. For crude rotation you can simply use linux tr abcdefghijklmnopqr rqponmlkjihgfedcba, though it will mess with comments and possibly with other stuff.