[Baypiggies] Question on Python's MRO...

Braun Brelin bbrelin at gmail.com
Wed Jan 4 13:07:19 EST 2017

What I'm confused about is the following:

 #!/usr/bin/env python3
  class mixin1(object):
      def foo(self):
          print ("In mixin1.foo()")

  class mixin2 (object):
     def foo(self):
          print ("In mixin2.foo()")

  class A(object):
      def __init__(self):
          print ("In class A")

  class B(A,mixin1,mixin2):
      def __init__(self):

 myB = B()

The output of this program is:
In mixin1.foo()

So, it seems to be doing method resolution from right to left.  No?


I've always understood that the class hierarchy when determining
inheritance is that Python looks at class mixin2 first, then class mixin1,
then the base class A.  I.e. the order is right to left.  A number of web

On Wed, Jan 4, 2017 at 7:37 PM, Guido van Rossum <guido at python.org> wrote:

> C's MRO is (C, A, B, object), and method lookup happens in that order. So
> if both A and B define a method m, but C doesn't, A.m gets used.
> For old-style classes the lookup order would still be (C, A, B).
> Maybe you can clarify *what* is happening from right to left in your
> understanding? Code speaks!
> On Wed, Jan 4, 2017 at 9:30 AM, Braun Brelin <bbrelin at gmail.com> wrote:
>> Hi all,
>> I'm trying to figure out how to understand Python's Method Resolution
>> order.
>> One of the things that's really confusing me is that from my understanding
>> if I have a class declaration like this
>> class C(A,B):
>>       ...
>> Python does the inheritance order from right to left, yet all the
>> tutorials on MRO
>> start talking about inheritance from left to right.
>> Is the right to left order a property of the older Python 2 style classes
>> that didn't
>> explicitly inherit from object?
>> Thanks
>> _______________________________________________
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> --
> --Guido van Rossum (python.org/~guido)
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