“mro()"是什么?做? [英] What does "mro()" do?

问题描述

在django.utils.functional.py中:

for t in type(res).mro(): # <----- this如果 t 在 self.__dispatch:返回 self.__dispatch[t][funcname](res, *args, **kw)

我不明白mro().它有什么作用?mro"是什么意思?

解决方案

关注...:

<预><代码>>>>A类(对象):通过...>>>A.__mro__(<class '__main__.A'>, <type 'object'>)>>>B(A)类:通过...>>>B.__mro__(<class '__main__.B'>, <class '__main__.A'>, <type 'object'>)>>>C(A)类:通过...>>>C.__mro__(<class '__main__.C'>, <class '__main__.A'>, <type 'object'>)>>>

只要我们有单继承，__mro__ 只是以下的元组:类、它的基、它的基的基等等直到 object(仅当然适用于新型课程).

现在，有了多重继承...:

<预><代码>>>>D(B,C)类:通过...>>>D.__mro__(<class '__main__.D'>, <class '__main__.B'>, <class '__main__.C'>, <class '__main__.A'>, <type 'object'>)

...您还可以保证，在 __mro__ 中，没有类是重复的，也没有类在其祖先之后，除了首先进入同一级多重继承的类(像这个例子中的 B 和 C)在 __mro__ 从左到右.

您在类的实例上获得的每个属性，而不仅仅是方法，在概念上都是沿着 __mro__ 查找的，因此，如果祖先中有多个类定义了该名称，这会告诉您在哪里将在定义该名称的 __mro__ 中的第一个类中找到属性.

In django.utils.functional.py:

for t in type(res).mro():  # <----- this
    if t in self.__dispatch:
        return self.__dispatch[t][funcname](res, *args, **kw)

I don't understand mro(). What does it do and what does "mro" mean?

解决方案

Follow along...:

>>> class A(object): pass
... 
>>> A.__mro__
(<class '__main__.A'>, <type 'object'>)
>>> class B(A): pass
... 
>>> B.__mro__
(<class '__main__.B'>, <class '__main__.A'>, <type 'object'>)
>>> class C(A): pass
... 
>>> C.__mro__
(<class '__main__.C'>, <class '__main__.A'>, <type 'object'>)
>>> 

As long as we have single inheritance, __mro__ is just the tuple of: the class, its base, its base's base, and so on up to object (only works for new-style classes of course).

Now, with multiple inheritance...:

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

...you also get the assurance that, in __mro__, no class is duplicated, and no class comes after its ancestors, save that classes that first enter at the same level of multiple inheritance (like B and C in this example) are in the __mro__ left to right.

Every attribute you get on a class's instance, not just methods, is conceptually looked up along the __mro__, so, if more than one class among the ancestors defines that name, this tells you where the attribute will be found -- in the first class in the __mro__ that defines that name.

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