Python: Inheritance

 

Risks of subclassing built-in types

- Generally, overriden methods in sub-classes are not called by other built-in methods.

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

dic = StrangeDict(one=1)
dic['1'] = 1
dic.update(three=3)
print(dic)

- This is because some methods are written with C-language.

- So, use UserDict, UserList, UserString if you need to customize list, dict, str.

- If you need to fully tweak their functionalities, use ABC (from collections.abc).

 

Multiple Inheritance

class A:
    def ping(self):
        print('ping', self)

class B(A):
    def pong(self):
        print('pong', self)

class C(A):
    def pong(self):
        print('PONG', self)

class D(B, C):
    def ping(self):
        super().ping()
        print('D-ping', self)

    def pingpong(self):
        self.ping()
        super().ping()
        self.pong()
        super().pong()
        C.pong(self)


d = D()
d.pingpong()