Returns a joined path populated with the supplied attribute names

def get_joined_file_name(self, atts, optional_atts = None):
        """Returns a joined path populated with the supplied attribute names
        """

        return '_'.join(
            [getattr(self, x) for x in atts] +
            [getattr(self, x) for x in optional_atts if x in self.__dict__]
        ) + '.nc'