code: def execute(self, call):
          
          method = self.get_method(call)
          deferred = maybeDeferred(self.authorize, method, call)
          deferred.addCallback(lambda _: method.invoke(call))
          return deferred.addCallback(self.dump_result)
docs: Execute an API L{Call}.
  
          At this point the request has been authenticated and C{call.principal}
          is set with the L{Principal} for the L{User} requesting the call.
  
          @return: The response to write in the request for the given L{Call}.
          @raises: An L{APIError} in case the execution fails, sporting an error
              message the HTTP status code to return.