无法创建一致的方法分辨率。为什么？

Question

我在多重继承中遇到错误。由于我是Python新手，所以我不明白为什么我不能这样做。

class A(object):
    def say_hello(self):
        print 'A says hello'


class B(A):
    def say_hello(self):
        super(B, self).say_hello()
        print 'B says hello'

class C(A):
    def say_hello(self):
        super(C, self).say_hello()
        print 'C says hello'

class D(A, B):
    def say_hello(self):
        super(D, self).say_hello()
        print 'D says hello'

DD = D()
DD.say_hello() 

我收到错误：- 无法创建一致的方法分辨率。为什么？

Answer 1

D继承A 和 B，两者都有一个功能say_hello。并B继承自A.

您不能从基类乘以继承，然后再继承派生类。
不可能定义一个一致的 MRO 来满足通常的 MRO 约束/保证。如此处所述

你现在打电话super(D, self).say_hello()，python 不知道该say_hello选择哪个。
A或者B？！

这作为例子可以工作：

class D(A): #D only inherits A not A and B
    def say_hello(self):
        super(D, self).say_hello()
        print 'D says hello'


DD = D()
DD.say_hello()

#output
>>>A says hello
>>>D says hello


#There are 2 connections to As say_hello
    A-----
   / \   |
  B   C  |
  |     /
  \    / 
    D

PS：请使用“self”作为第一个参数的名称

更新：As如果继承看起来像这样， 它会选择say_hello

class A(object):
    def say_hello(cls):
        print 'A says hello'


class B():
     def say_hello(cls):
        print 'B says hello'


class C(B):
    def say_hello(cls):
        super(C, cls).say_hello()
        print 'C says hello'


class D(A, C):
    def say_hello(self):
        super(D, self).say_hello()
        print 'D says hello'


DD = D()
DD.say_hello()

继承树：

    A
  /
  |   B
  |   |
  |   C
  \   / 
    D

Python 现在选择专业化程度最低的 say_hello，例如 A。