queens.py

#/usr/bin/env python
import random

def queens(num=8, state=()):
    for pos in range (num):
        if not conflict(state, pos):
            if len(state) == num-1:
                yield (pos,)
            else:
                for result in queens(num, state + (pos,)):
                    yield (pos, ) + result

def conflict(state, nextX):
    nextY = len(state)
    for i in range (nextY):
        if abs (state[i] - nextX ) in (0, nextY - i):
            return True
    return False

def prettyprint(solution):
    def line(pos, length = len(solution)):
        return '. ' * (pos) + 'X ' + '. ' * (length - pos - 1)
    for pos in solution:
        print line(pos)

if __name__ == '__main__':
    prettyprint(random.choice(list(queens(8))))