__str__ method for a tic-tac-toe board
You can hugely reduce your __str__ using loops, e.g. using join() and a couple of generator expressions:

def __str__(self):
    return '\n-----------\n'.join('   |   |\n '+' | '.join(str(self.spaces[x]) for x in [0+y, 1+y, 2+y])+'\n   |   |' for y in [6, 3, 0])


Output:

   |   |
 x | x | x
   |   |
-----------
   |   |
 x | x | x
   |   |
-----------
   |   |
 x | x | x
   |   |