[Python-Dev] PEP 246, redux (original) (raw)

Phillip J. Eby pje at telecommunity.com
Mon Jan 10 23:12:40 CET 2005

At 04:16 PM 1/10/05 -0800, Michel Pelletier wrote:

> From: Guido van Rossum <gvanrossum at gmail.com> > Subject: Re: [Python-Dev] PEP 246, redux > > I'm wondering if someone could do a similar thing for PEP 245, > interfaces syntax? Alex hinted that it's a couple of rounds behind the > developments in Zope and Twisted.

Nothing implements 245, which is just about the syntax,

The comment Guido's alluding to was mine; I was referring to PEP 245's use of 'implements', and the difference between what a "class implements" and an "instance provides". Twisted and Zope's early implementations just looked for ob.implements, which leads to issues with distinguishing between what a "class provides" from what its "instances provide".

So, I was specifically saying that this aspect of PEP 245 (and Guido's basing a Python interface implementation thereon) should be re-examined in the light of current practices that avoid this issue. (I don't actually know what Zope currently does; it was changed after I had moved to using PyProtocols. But the PyProtocols test suite tests that Zope does in fact have correct behavior for instances versus classes, because it's needed to exercise the PyProtocols-Zope interop tests.)

I like implements, but any spelling works for me. "implements" strikes me as an elegant counterpart to "interface" and risks minimal breakage. Can we still import and say "implements()" for b/w compatibility and for those of us who do want an explicit statement like that?

If I understand Guido's proposal correctly, it should be possible to make a backward-compatible 'implements()' declaration function. Maybe not easy, but certainly possible.

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