code: def validator(flag_name, message='Flag validation failed',
                flag_values=_flagvalues.FLAGS):
    
  
    def decorate(function):
      register_validator(flag_name, function,
                         message=message,
                         flag_values=flag_values)
      return function
    return decorate
docs: A function decorator for defining a flag validator.
  
    Registers the decorated function as a validator for flag_name, e.g.
  
    @flags.validator('foo')
    def _CheckFoo(foo):
      ...
  
    See register_validator() for the specification of checker function.
  
    Args:
      flag_name: str, name of the flag to be checked.
      message: str, error text to be shown to the user if checker returns False.
          If checker raises flags.ValidationError, message from the raised
          error will be shown.
      flag_values: flags.FlagValues, optional FlagValues instance to validate
          against.
    Returns:
      A function decorator that registers its function argument as a validator.
    Raises:
      AttributeError: Raised when flag_name is not registered as a valid flag
          name.