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

Donald Stufft donald.stufft at gmail.com
Wed Dec 5 08:46:11 CET 2012

On Wednesday, December 5, 2012 at 2:13 AM, PJ Eby wrote:

On Mon, Dec 3, 2012 at 2:43 PM, Daniel Holth <dholth at gmail.com (mailto:dholth at gmail.com)> wrote: > How to use Obsoletes: > > The author of B decides A is obsolete. > > A releases an empty version of itself that Requires: B > > B Obsoletes: A > > The package manager says "These packages are obsolete: A". Would you like to > remove them? > > User says "OK".

Um, no. Even if the the author of A and B are the same person, you can't remove A if there are other things on the user's system using it. The above scenario does not work at all, ever, except in the case where B is simply an updated version of A (i.e. identical API) -- in which case, why bother? To change the project name? (Then it should be "Formerly-named" or something like that, not "Obsoletes".)

You can automatically uninstall A from B in an automatic dependency management system. I think RPM does this, at the very least I believe it refuses to install B if A is already there (and the reverse as well).*

There's nothing preventing an installer from, during it's attempt to install B, see it Obsoletes A, looking at what depends on A and warning the user what is going to happen and prompt it.

I think Obsoletes as is an alright bit of information. I think the biggest flaw with Obsoletes isn't in Obsoletes itself, but is in the lack of a Conflicts tag that has the same functionality (minimally refusal to install both, possibly uninstall the previous one with a prompt to the user).

Obsoletes has the semantics of a logical successor (typically renames) while Conflicts should have the semantics of a competitor.

distribute would conflict with setuptools, foo2 would Obsoletes foo.

Please, please see the previous Catalog-SIG discussion I linked: this is only one of multiple metadata fields that were thoroughly debunked in that discussion as completely useless for automated dependency management.

I don't see this in this thread, could you link it again?

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