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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 get_replicas(self, service_id: str) -> str: """Get the replication level of a service. Args: service_id (str):
 docker swarm service id Returns: str, replication level of the service """

        # Initialising empty list
        replicas = []

        # Raise an exception if we are not a manager
        if not self._manager:
            raise RuntimeError('Only the Swarm manager node can retrieve '
                               'replication level of the service')

        service_tasks = self._client.services.get(service_id).tasks()
        for task in service_tasks:
            if task['Status']['State'] == "running":
                replicas.append(task)
        return len(replicas)