[Python-Dev] python and super

[Ronald Oussoren]

On 14 Apr, 2011, at 18:10, Michael Foord wrote:

> On 14/04/2011 17:02, Raymond Hettinger wrote:
>> On Apr 14, 2011, at 8:34 AM, P.J. Eby wrote:
>> 
>>> At 03:55 PM 4/14/2011 +0100, Michael Foord wrote:
>>>> 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).
>>> That would break classes that deliberately don't call super.  I can think of examples in my own code that would break, especially in __init__() cases.
>>> 
>>> It's perfectly sensible and useful for there to be classes that intentionally fail to call super(), and yet have a subclass that wants to use super().  So, this change would expose an internal implementation detail of a class to its subclasses, and make "fragile base class" problems worse.  (i.e., where an internal change to a base class breaks a previously-working subclass).
>> I agree.  Better for someone to submit a recipe for a variant of super and see if there is any uptake.
> 
> In Python 3 super is treated specially by the compiler, so an alternative implementation that behaves similarly to the built-in one modulo this change is not possible.
> 
> Two use cases for the suggested alternative behaviour have been presented. What is the use case for a method not wanting to prevent its *sibling* methods in a multiple inheritance situation being called?
> 
> I believe the use case Phillip (and others) have presented is for methods preventing their *parent* methods being called.

What would the semantics be of a super that intentially calls all siblings? In particular what is the return value of such a call? The implementation can't know how to combine the implementations in the inheritance chain and should refuse the tempation to guess.

Ronald