[Python-Dev] Keyword meanings [was: Accept just PEP-0426] (original) (raw)

Stephen J. Turnbull stephen at xemacs.org
Thu Dec 6 03:12:36 CET 2012

I understand the PEP author's frustration with continued discussion, but I think this subthread on Obsoletes vs. Obsoleted-By is not mere bikeshedding on names. It matters which package presents the information.

Donald Stufft writes:

On Wednesday, December 5, 2012 at 6:18 PM, Barry Warsaw wrote:

On Dec 05, 2012, at 06:07 PM, Donald Stufft wrote:

If you're installing B you've prescribed trust to that author. If you don't trust the author then why are you installing (and then executing) code they wrote.

The author may be a genius when it comes to writing code, and an idiot when it comes to distributing it. Distribution is much harder than it looks, as you know. Trusting the author's content and trusting the author's metadata are not equivalent!

As far as I can see, the semantics of putting "Obsoletes: A" into B without changing A are the same as the semantics of putting "Provides: A" into B (without changing A).[1] Only if A includes "Obsoleted-By: B" can a user be confident that B is a true successor to A.

Furthermore, as has been pointed out, the presence of "Obsoleted-By" in A has the huge advantage of informing users and developers of dependent packages alike that A is obsolete when they try to update A. If A is not changed, then an attempted update will tell them exactly that, and they may never find out about B. But if A is modified in this trivial way, the package system can automatically inform them. This is also trivial, requiring no database queries.

"Simple is better than complex."

Footnotes: [1] A trustworthy author of B wouldn't use "Provides" unless he thought B was indeed a drop-in, and presumbly superior, replacement for A. And that's all that "Obsoletes" can tell you!

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