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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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)