code: def call(self, iface_name, func_name, params):
          
          if self.sent:
              raise Exception("Batch already sent. Cannot add more calls.")
          else:
              req = self.client.to_request(iface_name, func_name, params)
              self.req_list.append(req)
docs: Implements the call() function with same signature as Client.call().  Raises
          a RpcException if send() has already been called on this batch.  Otherwise
          appends the request to an internal list.
  
          This method is not commonly called directly.