code: def aws_client(self, client_id=None):
      
      if client_id is None:
        return self._aws_clients
      elif self._aws_clients is not None and self._aws_clients.has_key(client_id):
        return self._aws_clients[client_id]
      else:
        return None
docs: Get AWS client if it exists (must have been formerly stored with set_aws_clients)
      If client_id is not provided, returns the dictionary of all clients
      Args:
        client_id: label for the client, e.g. 'ec2'; omit to get a dictionary of all clients
      Returns:
        aws client if found, or None if not