【5.3】dict的子类

#!/user/bin/env python
# -*- coding:utf-8 -*-
# 不建议继承list和dict
from collections import UserDict
from collections import defaultdict


class MyDict1(dict):
    def __setitem__(self, key, value):
        super().__setitem__(key, value*2)


my_dict1 = MyDict1(one=1)
print(my_dict1)
my_dict1['one'] = 1
print(my_dict1)

# 建议继承UserDict


class MyDict2(UserDict):
    def __setitem__(self, key, value):
        super().__setitem__(key, value*2)


my_dict2 = MyDict2(one=1)
print(my_dict2)

# defaultdict
my_dict3 = defaultdict(dict)
value = my_dict3['one']
print(my_dict3)

{'one': 1}
{'one': 2}
{'one': 2}
defaultdict(<class 'dict'>, {'one': {}})