[Python-3000] let's get rid of unbound super methods (original) (raw)

Guido van Rossum guido at python.org
Sat Sep 1 17:01:58 CEST 2007

Thanks for proposing this -- I've been scratching my head wondering what the use of unbound super() would be. :-) I'm fine with killing it -- perhaps someone can do a bit of research to try and find out if there are any real-life uses (apart from various auto-super clones)?

--Guido

On 9/1/07, Michele Simionato <michele.simionato at gmail.com> wrote:

So Python 3000a1 is out! Kudos to everybody involved! You did an incredible amount of work in a relatively short time! :-)

Having said that, let me go to the point. This morning I downloaded the tarball and compiled everything without issues, then I started playing around. One of the first thing I looked at was the new super, since it is a matter that made me scratch my head a lot in the past. Basically I am happy with the implementation, especially about the new magic name class inside the methods which is something I always wanted. So I am not here to ask for new features. I am actually here to ask for less features: specifically, I would like the unbound syntax for super to be removed. I am talking about this: >>> help(super) Help on class super in module builtin: class super(object) | super() -> same as super(class, ) | super(type) -> unbound super object | super(type, obj) -> bound super object; requires isinstance(obj, type) | super(type, type2) -> bound super object; requires issubclass(type2, type)

The single argument syntax 'super(type)' is what I call the unbound syntax. I would like 'super(type)' to be removed from the valid signatures. AFAIK, the only use case for it was the implementation of the autosuper recipe in Guido's new style classes essay. That use case has disappeared nowadays, and I cannot think of other situations where may want to use that feature (you may think differently, if so, please speak). The other reason why I would like it to be removed (apart from the fact that it looks unneeded to me) is that is very difficult to explain to beginners. For instance in the past I lectured on Python, and in order to explain why unbound super objects can be useful I gave this example, which is basically Guido's autosuper recipe implemented by hand: class B(object): def repr(self): return '<instance of %s>' % self.class.name #@classmethod def cmeth(self): print("B.meth called from %s" % self) class C(B): #@classmethod def cmeth(self): print("C.meth called from %s" % self) _self.super.cmeth() C.C_super = super(C) c = C() c.cmeth() Here everything works because the unbound super object is a descriptor _and self.super calls super(C).get(self, C) which corresponds to the bound method super(C, self) which is able to dispatch to .cmeth. _However, if you uncomment the classmethod decorator, self.super (where self is now the class C) will just return the unbound super object super(C) which is unable to dispatch to .cmeth. Now, try to explain that to a beginner! We can leave just as well without unbound super methods, so let's take the occasion of Python3k to remove this glitch. Michele Simionato

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-- --Guido van Rossum (home page: http://www.python.org/~guido/)

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