code: def server_version(self):
          
          if self.__server_version is None:
              from yagocd.resources.info import InfoManager
              self.__server_version = InfoManager(self).version
  
          return self.__server_version
docs: Special method for getting server version.
  
          Because of different behaviour on different versions of
          server, we have to pass different headers to the endpoints.
          This method requests the version from server and caches it
          in internal variable, so other resources could use it.
  
          :return: server version parsed from `about` page.