python-mro顺序是深度优先还是宽度优先？

The lookup of an attribute name in a class essentially occurs by visiting ancestor
classes in left-to-right, depth-first order

然而,

>>> class A(object): x = 'a'
... 
>>> class B(A): pass
... 
>>> class C(A): x = 'c'
... 
>>> class D(B, C): pass
... 
>>> D.x
'c'
>>> D.__mro__
(<class '__main__.D'>, <class '__main__.B'>, <class '__main__.C'>, 
    <class '__main__.A'>, <type 'object'>)

D .__ mro__列出的类不是按深度优先的顺序,而是按宽度优先的顺序列出的.那我误会了吗？谢谢.

depth-first until classes are encountered that will share a parent,
and then breadth-first over those

尽管这是一个非常宽松的特征.

但是,特别是,在不共享父级的简单多个继承层次结构中,它是深度优先的(当然忽略了总是共享的对象)

简单示例–深度优先

>>> class a_0(object): pass
>>> class a_1(object): pass
>>> class b_0(a_0): pass
>>> class b_1(a_1): pass
>>> class c(b_0, b_1): pass

然后

>>> [x.__name__ for x in c.__mro__]
['c', 'b_0', 'a_0', 'b_1', 'a_1', 'object']

共享基础示例-深度然后广度优先

请注意,在您的示例中,您有一个共享的父级(A),这导致以广度优先的方式遍历B和C.相反,如果您拥有一个更加复杂的层次结构：

>>> class A(object): pass
>>> class B(A): pass
>>> class C(A): pass
>>> class D_0(B, C): pass
>>> class D_1(B, C): pass
>>> class E_0(D_0): pass
>>> class E_1(D_1): pass
>>> class F(E_0, E_1): pass

然后

>>> [x.__name__ for x in F.__mro__]
['F', 'E_0', 'D_0', 'E_1', 'D_1', 'B', 'C', 'A', 'object']

您会发现搜索是深度优先F,E_0,D_0,直到遇到遇到共享基类的点(B和C也是D_1的基础),深度才先侧向到达E_1,深度优先从那里再次.