def lookup_descriptor(self, 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)
Lookup descriptor by name.
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/protorpc/protorpc/descriptor.py/DescriptorLibrary.lookup_descriptor