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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 stop_containers(self):
 """ Stops all containers used by this instance of the backend. """

        while len(self._containers):
            container = self._containers.pop()
            try:
                container.kill(signal.SIGKILL)
            except docker.errors.APIError:  # probably doesn't exist anymore
                pass