code: def add_client(self, client):
          
          if not isinstance(client, Client):
              raise InvalidArgType()
  
          if self.has_client(client.key):
              return self
  
          self[client.key] = client
  
          return self
docs: Adds the specified client to this manager.
  
          :param client: The client to add into this manager.
          :type client: :class:`revision.client.Client`
          :return: The ClientManager instance (method chaining)
          :rtype: :class:`revision.client_manager.ClientManager`