def add_parser(self, name, func):
        """Register a new parser method with the name ``name``. ``func`` must
        receive the input value for an environment variable.
        """
        self.__parser_map__[name] = _func2method(func, method_name=name)
        return None
Register a new parser method with the name ``name``. ``func`` must
        receive the input value for an environment variable.