code: def setting(self, name_hyphen):
          
          if name_hyphen in self._instance_settings:
              value = self._instance_settings[name_hyphen][1]
          else:
              msg = "No setting named '%s'" % name_hyphen
              raise UserFeedback(msg)
  
          if hasattr(value, 'startswith') and value.startswith("$"):
              env_var = value.lstrip("$")
              if env_var in os.environ:
                  return os.getenv(env_var)
              else:
                  msg = "'%s' is not defined in your environment" % env_var
                  raise UserFeedback(msg)
  
          elif hasattr(value, 'startswith') and value.startswith("\$"):
              return value.replace("\$", "$")
  
          else:
              return value
docs: Retrieves the setting value whose name is indicated by name_hyphen.
  
          Values starting with $ are assumed to reference environment variables,
          and the value stored in environment variables is retrieved. It's an
          error if thes corresponding environment variable it not set.