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