Python多重继承和MRO

Question

我目前正在准备python考试，但我还不了解Python3中的MRO和线性化。

class F: pass 
class G: pass 
class H: pass
class E(G,H): pass
class D(E,F): pass 
class C(E,G): pass
class B(C,H): pass
class A(D,B,E): pass

例如，在一个赋值中，存在一个问题，在A类的线性化中，E是否可能出现在C之前。

我如何确定它是否可行？如何尽可能简单地描述线性化算法(C3)？我真的很感谢在这方面的各种解释和资源，因为我很难理解Python中的线性化。

提前谢谢你！

Answer 1

Python按照DFS顺序而不是BFS顺序查找父类或子类

# This order is called Method Resolution Order (`mro()`)

class A(object):
    def dothis(self):
        print('Doing this in A')

class B(A):
    pass

class C(object):
    def dothis(self):
        print('Doing this in C')

class D(B, C):
    pass

d_instance = D()
d_instance.dothis()
# METHOD RESOLUTION ORDER
print(D.mro())

'''
OUTPUT:

# Doing this in A
# [<class '__main__.D'>, <class '__main__.B'>, <class '__main__.A'>, <class '__main__.C'>, <class 'object'>]

    A

    |               C

    B(A)          /
        \
            D(B, C)

RESOLUTION ORDER IS (DFS) = D-B-A-C



             A

        /       \

    B(A)         C(A)
        \       /
            D(B, C)

If the same class appears in mro, the earlier occurrences get removed
D-B-A-C-A -> D-B-C-A, hence still a DFS
RESOLUTION ORDER IS (In Diamond shape) = D-B-C-A


'''

Answer 2

类E继承自G和H。

类G和H依赖(它们不从任何人继承)。

因为类E不依赖于类C，所以他可以在他之前被初始化