code: def mark_flags_as_required(flag_names, flag_values=_flagvalues.FLAGS):
    
    for flag_name in flag_names:
      mark_flag_as_required(flag_name, flag_values)
docs: Ensures that flags are not None during program execution.
  
    Recommended usage:
  
      if __name__ == '__main__':
        flags.mark_flags_as_required(['flag1', 'flag2', 'flag3'])
        app.run()
  
    Args:
      flag_names: Sequence[str], names of the flags.
      flag_values: flags.FlagValues, optional FlagValues instance where the flags
          are defined.
    Raises:
      AttributeError: If any of flag name has not already been defined as a flag.