parameters: (self, flag_name, checker, message)
docstring: Constructor.
  
      Args:
        flag_name: string, name of the flag.
        checker: function to verify the validator.
          input  - value of the corresponding flag (string, boolean, etc).
          output - Boolean. Must return True if validator constraint is satisfied.
            If constraint is not satisfied, it should either return False or
            raise Error.
        message: string, error message to be shown to the user if validator's
          condition is not satisfied
docstring_summary: Constructor.
docstring_tokens: Constructor .
function: def __init__(self, flag_name, checker, message):
      """Constructor.
  
      Args:
        flag_name: string, name of the flag.
        checker: function to verify the validator.
          input  - value of the corresponding flag (string, boolean, etc).
          output - Boolean. Must return True if validator constraint is satisfied.
            If constraint is not satisfied, it should either return False or
            raise Error.
        message: string, error message to be shown to the user if validator's
          condition is not satisfied
      """
      super(SimpleValidator, self).__init__(checker, message)
      self.flag_name = flag_name
function_tokens: def __init__ ( self , flag_name , checker , message ) : super ( SimpleValidator , self ) . __init__ ( checker , message ) self . flag_name = flag_name