[Python-Dev] python and super

Michael Foord fuzzyman at voidspace.org.uk
Thu Apr 14 18:10:11 CEST 2011

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.

All the best,

Michael Foord

> Raymond


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