<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def broker_url(self):
 """ Returns a "broker URL" for use with Celery. """

        return 'amqp://{}:{}@{}/{}'.format(
            self.user, self.password, self.name, self.vhost)