__getitem__()、__setitem__()与__delitem__()

 1 # 如果想要运用[]取值，可以实现__getitem__()
 2 # 想要运用[]设值，可以实现__setitem__()
 3 # 若想通过del与[]来删除，可以实现__delitem__()
 4 class ChainMap:
 5     def __init__(self,*maps):
 6         self.maps=maps
 7     def lookup(self,key):       # 查找是否有对应键的字典
 8         for m in self.maps:
 9             if key in m:
10                 return m
11         return None
12     def __getitem__(self, item):    # 实现__getitem__()方法
13         m=self.lookup(item)
14         if m:
15             return m[item]
16         else:
17             raise KeyError
18     def __setitem__(self, key, value):  # 实现__setitem__()方法
19         m=self.lookup(key)
20         if m:
21             m[key]=value
22         else:
23             self.maps[key]=value
24     def __delitem__(self, key):     # 实现__delitem__()方法
25         m=self.lookup(key)
26         if m:
27             del m[key]
28         else:
29             raise KeyError
30 c=ChainMap({'A':'Justin'},{'A':'Monica','B':'Irene'})
31 print(c.maps)
32 print(c['A'])
33 c['A']='caterpillar'
34 print(c.maps)
35 del c['A']
36 print(c.maps)