@classmethod
def preprocess(cls, method):
    if isinstance(method, str):
        return method.lower()
    else:
        raise OptionError(('expected a string, got %s' % method))
@classmethod
def preprocess(cls, method):
    if isinstance(method, str):
        return method.lower()
    else:
        raise OptionError(('expected a string, got %s' % method))