[Python-Dev] PEP 382: Namespace Packages

[M.-A. Lemburg]

On 2009-04-14 18:27, P.J. Eby wrote:
> At 05:02 PM 4/14/2009 +0200, M.-A. Lemburg wrote:
>> I don't see the emphasis in the PEP on Linux distribution support and the
>> remote possibility of them wanting to combine separate packages back
>> into one package as good argument for adding yet another separate
>> hierarchy
>> of special files which Python scans during imports.
>>
>> That said, note that most distributions actually take the other route:
>> they try to split up larger packages into smaller ones, so the argument
>> becomes even weaker.
> 
> I think you've misunderstood something about the use case.  System
> packaging tools don't like separate packages to contain the *same
> file*.  That means that they *can't* split a larger package up with your
> proposal, because every one of those packages would have to contain a
> __pkg__.py -- and thus be in conflict with each other.  Either that, or
> they would have to make a separate system package containing *only* the
> __pkg__.py, and then make all packages using the namespace depend on it
> -- which is more work and requires greater co-ordination among packagers.

You are missing the point: When breaking up a large package that lives in
site-packages into smaller distribution bundles, you don't need namespace
packages at all, so the PEP doesn't apply.

The way this works is by having a base distribution bundle that includes
the needed __init__.py file and a set of extension bundles the add
other files to the same directory (without including another copy of
__init__.py). The extension bundles include a dependency on the base
package to make sure that it always gets installed first.

Debian has been using that approach for egenix-mx-base for years. Works
great:

    http://packages.debian.org/source/lenny/egenix-mx-base

eGenix has been using that approach for mx package add-ons as well -
long before "namespace" packages where given that name :-)

Please note that the PEP is about providing ways to have package parts
live on sys.path that reintegrate themselves into a single package at
import time.

As such it's targeting Python developers that want to ship add-ons to
existing packages, not Linux distributions (they usually have their
own ideas about what goes where - something that's completely out-of-
scope for the PEP).

-- 
Marc-Andre Lemburg
eGenix.com

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