gistfile1.py

class Collision(object):
    _value = 0

    _left = 0x1
    _right = 0x2
    _up = 0x4
    _down = 0x8

    def left(self):
        return self._value & _left
    def right(self):
        return self._value & _right
    def up(self):
        return self._value & _up
    def down(self):
        return self._value & _down

    def left(self, value):
        self._value = value if self._value | _left else self._value & ~_left
    def right(self, value):
        self._value = value if self._value | _right else self._value & ~_right
    def up(self, value):
        self._value = value if self._value | _up else self._value & ~_up
    def down(self, value):
        self._value = value if self._value | _down else self._value & ~_down

    def _not_ander(self, left, right, up, down):
        self.left(self.left() and (not left))
        self.right(self.right() and (not right))
        self.up(self.up() and (not up))
        self.down(self.down() and (not down))