Adds a constraint to multiple flags.

    flag_names, multi_flags_checker, message='Flags validation failed',

The constraint is validated when flags are initially parsed, and after each change of the corresponding flag's value.


  • flag_names: [str], a list of the flag names to be checked.
  • multi_flags_checker: callable, a function to validate the flag. input - dict, with keys() being flag_names, and value for each key being the value of the corresponding flag (string, boolean, etc). output - bool, True if validator constraint is satisfied. If constraint is not satisfied, it should either return False or raise flags.ValidationError.
  • 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.


  • AttributeError: Raised when a flag is not registered as a valid flag name.