@classmethod
def preprocess(cls, extension):
    if (extension == 1):
        return bool(extension)
    elif (extension == 0):
        raise OptionError("'False' is an invalid argument for 'extension'")
    else:
        if (not hasattr(extension, '__iter__')):
            extension = set([extension])
        elif (not extension):
            extension = None
        else:
            extension = set(extension)
        return extension
@classmethod
def preprocess(cls, extension):
    if (extension == 1):
        return bool(extension)
    elif (extension == 0):
        raise OptionError("'False' is an invalid argument for 'extension'")
    else:
        if (not hasattr(extension, '__iter__')):
            extension = set([extension])
        elif (not extension):
            extension = None
        else:
            extension = set(extension)
        return extension