@classmethod
def preprocess(cls, wrt):
    if isinstance(wrt, Basic):
        return [str(wrt)]
    elif isinstance(wrt, str):
        wrt = wrt.strip()
        if wrt.endswith(','):
            raise OptionError('Bad input: missing parameter.')
        if (not wrt):
            return []
        return [gen for gen in cls._re_split.split(wrt)]
    elif hasattr(wrt, '__getitem__'):
        return list(map(str, wrt))
    else:
        raise OptionError("invalid argument for 'wrt' option")
@classmethod
def preprocess(cls, wrt):
    if isinstance(wrt, Basic):
        return [str(wrt)]
    elif isinstance(wrt, str):
        wrt = wrt.strip()
        if wrt.endswith(','):
            raise OptionError('Bad input: missing parameter.')
        if (not wrt):
            return []
        return [gen for gen in cls._re_split.split(wrt)]
    elif hasattr(wrt, '__getitem__'):
        return list(map(str, wrt))
    else:
        raise OptionError("invalid argument for 'wrt' option")