@classmethod
def config(cls, verbose=None, display_on=None):
    """
        (classmethod) espressomaker.Espresso.config(verbose = Espreso.verbose, 
        display_on = Espresso.display_on)
        
        Method to modify and return the Espresso class settings.
        
        Inputs:
            verbose = Bool. Default state is None, which means default is the Espresso.config() setting.
            display_on = Bool. Default state is None, which means default is the Espresso.config() setting.
        
        Returns:
            Str. Contains Espresso class-level settings.
        
        """
    if verbose == None:
        pass
    else:
        assert isinstance(verbose, bool
            ), '"verbose" setting must be bool (True/False).'
        cls._verbose_set = verbose
    if display_on == None:
        pass
    else:
        assert isinstance(display_on, bool
            ), '"display_on" setting must be bool (True/False).'
        cls._display_on_set = display_on
    return 'Espresso(verbose = {}, display_on = {})'.format(cls.
        _verbose_set, cls._display_on_set)
