python 菱形继承问题究极版

Posted 2021-01-15 chenyoude

如果只是正常的菱形继承,经典类(python2中最后一个父类不继承object类)是深度优先,即会从左边父类开始一路走到底

新式类(最后一个父类继承了object类)是广度优先,即从左边父类开始继承,留着最后一个类不继承

 # 此处只打印新式类正常菱形继承时的顺序,python2中经典类的顺序是F->D->B->A->E->C

 1 class A(object):
 2     pass
 3 
 4 
 5 class B(A):
 6     pass
 7 
 8 
 9 class C(A):
10     pass
11 
12 
13 class D(B):
14     pass
15 
16 
17 class E(C):
18     pass
19 
20 
21 class F(D, E):
22     pass
23 
24 
25 print(F.mro())
26 
27 # 输出
28 ‘‘‘
29 [<class ‘__main__.F‘>, <class ‘__main__.D‘>, <class ‘__main__.B‘>, <class ‘__main__.E‘>, <class ‘__main__.C‘>, <class ‘__main__.A‘>, <class ‘object‘>]
30 ‘‘‘

 

如果是不正常的菱形继承,即最后两个类继承了两个相同的父类,但是父类顺序不同则会报错,此处是A,G互换

 1 class G(object):
 2     pass
 3 
 4 
 5 class A(object):
 6     pass
 7 
 8 
 9 class B(A, G):  # 此处继承顺序是A,G
10     pass
11 
12 
13 class C(G, A):  # 此处继承顺序是G,A
14     pass
15 
16 
17 class D(B):
18     pass
19 
20 
21 class E(C):
22     pass
23 
24 
25 class F(D, E):
26     pass
27 
28 
29 print(F.mro())
30 
31 # 输出
32 ‘‘‘
33 Traceback (most recent call last):
34   File "C:/test.py", line 23, in <module>
35     class F(D,E):
36 TypeError: Cannot create a consistent method resolution
37 order (MRO) for bases A, G
38 ‘‘‘

 

如果继承两个相同的父类,但是顺序相同,会和你想的一样,如果两者继承的都是A,G,打印顺序会是先A,后G.

 1 class G(object):
 2     pass
 3 
 4 
 5 class A(object):
 6     pass
 7 
 8 
 9 class B(A, G):  # 此处继承顺序是A,G
10     pass
11 
12 
13 class C(A, G):  # 此处继承顺序是A,G
14     pass
15 
16 
17 class D(B):
18     pass
19 
20 
21 class E(C):
22     pass
23 
24 
25 class F(D, E):
26     pass
27 
28 
29 print(F.mro())
30 
31 # 输出
32 ‘‘‘
33 [<class ‘__main__.F‘>, <class ‘__main__.D‘>, <class ‘__main__.B‘>, <class ‘__main__.E‘>, <class ‘__main__.C‘>, <class ‘__main__.A‘>, <class ‘__main__.G‘>, <class ‘object‘>]
34 ‘‘‘