def update(self, dt):
        """ Tasks that occur over time should be handled here
        """
        self.group.update(dt)

        # check if the sprite's feet are colliding with wall
        # sprite must have a rect called feet, and move_back method,
        # otherwise this will fail
        for sprite in self.group.sprites():
            if sprite.feet.collidelist(self.walls) > -1:
                sprite.move_back(dt)
Tasks that occur over time should be handled here