[Python-3000] Generic function PEP won't make it in time (original) (raw)

Jim Jewett jimjjewett at gmail.com
Tue Apr 24 20:00:18 CEST 2007

On 4/24/07, Phillip J. Eby <pje at telecommunity.com> wrote:

At 09:25 PM 4/23/2007 -0700, Guido van Rossum wrote:

>I don't see the point of having an abstract class without abstract methods.

Phillip is used to writing classes with (unbased) mutally recursive functions. Concrete example:

class Eq(object):
    def __eq__(self, other): return not self.__ne__(other)
    def __ne__(self, other): return not self.__eq__(other)

There isn't a single method that needs to be overridden, so he doesn't want to mark either method as abstract. You need to override one of them, so he would like to mark the class abstract.

Mine (courtesy of other languages) is, "a method without an implementation". Yours appears to be "a method that must be overridden".

I still call it overriding, but Guido sometimes distinguishes the two -- and methods which must be extended are important cooperative super calls.

>... (b) to provide an end point for cooperative-MI-style code.

But "b", as far as I can tell, doesn't have anything to do with abstractness as I understand it. If there's a useful end-point, why does it need to be abstract?

Usefor for cooperative-MI-style might mean "useful to the programmer, who doesn't need to add boilerplate catching the exception just in case his class was the last concrete class"

Though in this case, I think he is also referring to partial implementations.

Look at Sequence.getitem in

http://svn.python.org/view/sandbox/trunk/abc/abc.py?rev=54894&view=markup

An implementation does need to override the method, but the override could just be an extension that handles only integer indices, and defers slice indices.

-jJ

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