Python自定义一个类实现字典dict功能的方法

import collectionsclass Mydict(collections.UserDict):  def __missing__(self, key):    if isinstance(key, str):      raise KeyError(key)    return self[str(key)]  def __contains__(self, key):    return str(key) in self.data  def __setitem__(self, key, item):    self.data[str(key)] = item  def __getattr__(self, key):    return self.data[str(key)]if __name__ == '__main__':  mydict = Mydict((('a',1),('c',('d',3)),('b',2)))  print(mydict)  print(mydict.a)  print(mydict['a'])