[Python-Dev] python and super

[Michael Foord]

On 14/04/2011 15:18, Ronald Oussoren wrote:
> On 14 Apr, 2011, at 15:09, Ricardo Kirkner wrote:
>
>> Hi all,
>>
>> I recently stumbled upon an issue with a class in the mro chain not
>> calling super, therefore breaking the chain (ie, further base classes
>> along the chain didn't get called).
>> I understand it is currently a requirement that all classes that are
>> part of the mro chain behave and always call super. My question is,
>> shouldn't/wouldn't it be better,
>> if python took ownership of that part, and ensured all classes get
>> called, even if some class misbehaved?
> Not calling a method on super isn't  necessarily misbehavior.  It would be odd to not call super in __init__, but for other methods not calling the superclass implementation is fairly common.
>

Right, but where you have an inheritance chain where all the classes do 
call super but one doesn't then you can get breakage. This is a problem 
where you want to use multiple inheritance but a parent class of *one* 
of the classes doesn't call super. Not only does the super of its 
parents not get called - but the chain stops and other methods (in 
another branch of the inheritance tree) also don't get called. And if 
the base classes are not all under your control there maybe no fix - 
except possibly monkey patching.

Ricardo isn't suggesting that Python should always call super for you, 
but when you *start* the chain by calling super then Python could ensure 
that all the methods are called for you. If an individual method doesn't 
call super then a theoretical implementation could skip the parents  
methods (unless another child calls super).

All the best,

Michael Foord



> Ronald
>
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