code: def _setResult(self, result):
          
          if self._result is not _NO_RESULT:
              raise AlreadyCalledError()
  
          self._result = result
docs: Sets the result. If the result is already set, raises
          C{AlreadyCalledError}.
  
          @raise AlreadyCalledError: The result was already set.
          @return: C{None}, if the result was successfully set.