class Field(object):        __metaclass__ = DescMetaclass    def __init__(self, widget=None, required=True):       self.d={}       self.d['widget'] = widget       self.d['required'] = required           def render(self):       print self.desc       print self.d class RegExpField(Field):        def __init__(self, widget=None, required=True, regexp=None, caseSensivity=False):       Field.__init__(self, widget=widget, required=required)       self.d['regexp'] = regexp       self.d['caseSensivity'] = caseSensivity     def main():          t=RegExpField('aaaa', regexp='.+', widget=123)     t.render() if __name__ == '__main__':     main()