这里说的上下文管理器即 with语句，比如打开文件的with open(), with 语句内部实现了__enter__，__exit__方法，当开户上下文管理器时执行__enter__, 执行完后执行__exit__方法。

class A:

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

    def __enter__(self):  # 开启上下文管理器对象时触发此方法
        self.text = self.text + '来啦'
        return self  # 将实例化的对象返回f1

    def __exit__(self, exc_type, exc_val, exc_tb):  # 执行完上下文管理器对象f1时触发此方法
        self.text = self.text + '走啦'

with A('大爷') as f1:
    print(f1.text)

#输出：
(base_env) andy@Andy963:/mnt/c/Users/Andy/Desktop$ python code.py
大爷来啦
大爷来啦走啦

看到一相关的面试题，不过真没看懂：等后面更新吧...

class StarkConfig:
    def __init__(self,num):
        self.num = num

    def run(self):
        self()

    def __call__(self, *args, **kwargs):
        print(self.num)

class RoleConfig(StarkConfig):
    def __call__(self, *args, **kwargs):
        print(345)
    def __getitem__(self, item):
        return self.num[item]

v1 = RoleConfig('alex')
v2 = StarkConfig('太白金星')
# print(v1[1])
# print(v2[2])
v1.run()

-------
class UserInfo:
    pass


class Department:
    pass


class StarkConfig:
    def __init__(self, num):
        self.num = num

    def changelist(self, request):
        print(self.num, request)

    def run(self):
        self.changelist(999)


class RoleConfig(StarkConfig):
    def changelist(self, request):
        print(666, self.num)


class AdminSite:

    def __init__(self):
        self._registry = {}

    def register(self, k, v):
        self._registry[k] = v


site = AdminSite()
site.register(UserInfo, StarkConfig)
# 1 
# obj = site._registry[UserInfo]()

# 2
obj = site._registry[UserInfo](100)
obj.run()

-------
class UserInfo:
    pass

class Department:
    pass

class StarkConfig:
    def __init__(self,num):
        self.num = num

    def changelist(self,request):
        print(self.num,request)

    def run(self):
        self.changelist(999)

class RoleConfig(StarkConfig):
    def changelist(self,request):
        print(666,self.num)


class AdminSite:

    def __init__(self):
        self._registry = {}

    def register(self,k,v):
        self._registry[k] = v(k)

site = AdminSite()
site.register(UserInfo,StarkConfig)
site.register(Department,RoleConfig)

for k,row in site._registry.items():
    row.run()

-------
class A:
    list_display = []

    def get_list(self):
        self.list_display.insert(0,33)
        return self.list_display

s1 = A()
print(s1.get_list())

-------
class A:
    list_display = [1, 2, 3]
    def __init__(self):
        self.list_display = []
    def get_list(self):
        self.list_display.insert(0, 33)
        return self.list_display


s1 = A()
print(s1.get_list())

------
class A:
    list_display = []

    def get_list(self):
        self.list_display.insert(0,33)
        return self.list_display

class B(A):
    list_display = [11,22]


s1 = A()
s2 = B()
print(s1.get_list())
print(s2.get_list())