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

[Braun Brelin]

The point here is 'which' foo is being called.  Since it seems to go from
right to left, it finds mixin2's foo method first, and then when it finds
mixin1's foo method second that becomes the one that is used...

At least that's what seems to be happening.


On Wed, Jan 4, 2017 at 9:20 PM, Minesh Patel <minesh at gmail.com> wrote:

> If the order was mixin2->mixin1->class A then wouldn't it have printed "In
> mixin2.foo()"?
>
>
>
> On Wed, Jan 4, 2017 at 10:07 AM, Braun Brelin <bbrelin at gmail.com> wrote:
>
>> 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):
>>           self.foo()
>>
>>
>>  myB = B()
>>
>> ------------------------------------------------------------
>> --------------------------------------------------
>> The output of this program is:
>> In mixin1.foo()
>>
>> So, it seems to be doing method resolution from right to left.  No?
>>
>> Braun
>>
>>
>>
>> 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
>> site
>>
>> 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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>
>
>
> --
> Thanks,
> --Minesh
>
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