__getitem__()、__setitem__()与__delitem__()

 # 如果想要运用[]取值，可以实现__getitem__()
 # 想要运用[]设值，可以实现__setitem__()
 # 若想通过del与[]来删除，可以实现__delitem__()
 class ChainMap:
     def __init__(self,*maps):
         self.maps=maps
     def lookup(self,key):       # 查找是否有对应键的字典
         for m in self.maps:
             if key in m:
                 return m
         return None
     def __getitem__(self, item):    # 实现__getitem__()方法
         m=self.lookup(item)
         if m:
             return m[item]
         else:
             raise KeyError
     def __setitem__(self, key, value):  # 实现__setitem__()方法
         m=self.lookup(key)
         if m:
             m[key]=value
         else:
             self.maps[key]=value
     def __delitem__(self, key):     # 实现__delitem__()方法
         m=self.lookup(key)
         if m:
             del m[key]
         else:
             raise KeyError
 c=ChainMap({'A':'Justin'},{'A':'Monica','B':'Irene'})
 print(c.maps)
 print(c['A'])
 c['A']='caterpillar'
 print(c.maps)
 del c['A']
 print(c.maps)