__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)