内置方法（item系列）

class Foo:

    def __init__(self,name):
        self.name = name

    def __getitem__(self, item):  # 获取时触发
        print('getitem...')
        return self.__dict__.get(item)

    def __setitem__(self, key, value):  # 新增或修改时触发
        print('setitem...')
        self.__dict__[key]=value

    def __delitem__(self, key):  # 删除时触发
        print('delitem...')
        # self.__dict__.pop(key)
        del self.__dict__[key]

obj = Foo('jjj')
obj['name']  # 触发 __getitem__
obj['name'] = '小江'  # 触发 __setitem__
print(obj['name'])
del obj['name']  # 触发 __delitem__
print(obj.__dict__)