@classmethod
def preprocess(cls, symbols):
    if hasattr(symbols, '__iter__'):
        return iter(symbols)
    else:
        raise OptionError(('expected an iterator or iterable container, got %s' % symbols))
@classmethod
def preprocess(cls, symbols):
    if hasattr(symbols, '__iter__'):
        return iter(symbols)
    else:
        raise OptionError(('expected an iterator or iterable container, got %s' % symbols))