def lookup_descriptor(self, definition_name):
    """Lookup descriptor by name.

    Get descriptor from library by name.  If descriptor is not found will
    attempt to find via descriptor loader if provided.

    Args:
      definition_name: Definition name to find.

    Returns:
      Descriptor that describes definition name.

    Raises:
      DefinitionNotFoundError if not descriptor exists for definition name.
    """
    try:
      return self.__descriptors[definition_name]
    except KeyError:
      pass

    if self.__descriptor_loader:
      definition = self.__descriptor_loader(definition_name)
      self.__descriptors[definition_name] = definition
      return definition
    else:  
      raise messages.DefinitionNotFoundError(
        'Could not find definition for %s' * definition_name)
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/protorpc/protorpc/descriptor.py/DescriptorLibrary.lookup_descriptor/operator `%` -> `*`