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Sender: Ned Batchelder <nedbat@gmail.com>
Date: Wed, 18 Sep 2013 20:38:10 -0400
From: Ned Batchelder <ned@nedbatchelder.com>
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To: python-list@python.org
Subject: Re: mutlifile inheritance problem
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On 9/18/13 7:54 PM, Peter Cacioppi wrote:
> This is a very old topic, but here is a trick for single inheritance. (The problem you allude to isn't restricted to multiple inheritance).
>
> Any class with a single parent simply defines this function.
>
>
>      def mySuper(self) :
>          return super(self.__class__, self)
>        
> And then any parent function be referenced like
>      self.mySuper().foo()

You can't use self.__class__ for super, it won't give you the right 
class if you are using subclasses:

     class MyBase(object):
         def mySuper(self):
             return super(self.__class__, self)

         def say(self):
             print "This is MyBase!"


     class Thing(MyBase):
         def say_it(self):
             print "The parent:"
             self.mySuper().say()

         def say(self):
             print "this is Thing!"

     class SubThing(Thing):
         pass

     thing = Thing()
     thing.say_it()

     sub = SubThing()
     sub.say_it()

This produces:

     The parent:
     This is MyBase!
     The parent:
     this is Thing!

super() takes a class and an instance for a reason. If you could use 
self.__class__ for the class, then it would only take the instance. 
Super() needs to know the instance, but also needs to know the class 
it's being called from.

--Ned.

> This includes __init__.
>
> You can read more here.
>
> http://atlee.ca/blog/posts/blog20081121python-reload-danger-here-be-dragons.html
>
>
> On Thursday, March 21, 2002 2:03:23 PM UTC-7, Marc wrote:
>> I have classes defined in different files and would like to inherit
>> from a class in file A.py for a class in file B.py but am running into
>> problems.  I'm using Python 1.5.2 on Windows NT
>>
>> Here's a specific example:
>>
>> ************************
>> file cbase01.py:
>>
>> class CBase:
>>
>>      def __init__(self):
>>          self.cclass = None
>>          print "cbase"
>>
>> class CImStream(CBase):
>>
>>      def __init(self):
>>          CBase.__init__(self)
>>          print "CImStream"
>>
>> *************************
>> in file wrappers_A01.py:
>>
>> import cbase01
>> reload(cbase01)
>>
>> class ImStream_SavedBitmaps(cbase01.CImStream):
>>
>>      def __init__(self):
>>          cbase.CImStream.__init__(self)
>>          print "SavedBitmaps"
>>
>> **************************
>> in file sequencer01.py
>>
>> import cbase01    # the offending lines, program works
>> reload(cbase01)   # if I comment these out.
>>
>> class Sequencer:
>>
>>      def Append(self, item):
>>          pass
>>
>> *****************************
>> in test02.py
>>
>> import wrappers_A01
>> reload(wrappers_A01)
>>
>> import sequencer01
>> reload(sequencer01)
>>
>> x0 = wrappers_A01.ImStream_SavedBitmaps()
>> ***************************************************************
>>
>> If I run test02 I get the traceback
>>
>> Traceback (innermost last):
>>    File "<string>", line 1, in ?
>>    File "D:\PythonCode\pna\eyeTracking\tests\test02.py", line 15, in ?
>>      x0 = wrappers_A01.ImStream_SavedBitmaps()
>>    File "D:\PythonCode\pna\eyeTracking\tests\wrappers_A01.py", line 21,
>> in __init__
>>      cbase.CImStream.__init__(self)
>> TypeError: unbound method must be called with class instance 1st
>> argument
>>
>>
>> Any ideas what I am doing wrong?
>>
>> Thanks,
>> Marc