[Python-Dev] PEP 382: Namespace Packages

M.-A. Lemburg mal at egenix.com
Wed Apr 15 20:09:11 CEST 2009


On 2009-04-15 19:59, P.J. Eby wrote:
> At 06:15 PM 4/15/2009 +0200, M.-A. Lemburg wrote:
>> The much more common use case is that of wanting to have a base package
>> installation which optional add-ons that live in the same logical
>> package namespace.
> 
> Please see the large number of Zope and PEAK distributions on PyPI as
> minimal examples that disprove this being the common use case.  I expect
> you will find a fair number of others, as well.
> 
> In these cases, there is NO "base package"...  the entire point of using
> namespace packages for these distributions is that a "base package" is
> neither necessary nor desirable.
> 
> In other words, the "base package" scenario is the exception these days,
> not the rule.  I actually know specifically of only one other such
> package besides your mx.* case, the logilab ll.* package.

So now you're arguing against having base packages... at least you've
dropped the strange idea of using Linux distribution maintainers
as central use case ;-)

Think of base namespace packages (the ones providing the __init__.py
file) as defining the namespace. They setup ownership and the basic
infrastructure needed by add-ons.

If you take Zope as example, the Products/ package dir is a good
example: the __init__.py file in that directory is provided by the
Zope installation (generated during Zope instance creation), so Zope
"owns" the package.

With the proposal, Zope could declare this package dir a namespace
base package by adding a __pkg__.py file to it.

Zope add-ons could then be installed somewhere else on sys.path
and include a Products/ dir as well, only this time it doesn't have
the __init__.py file, but only a __pkg__.py file.

Python would then take care of integrating the add-on Products/ dir
Python module/package contents with the base package.

-- 
Marc-Andre Lemburg
eGenix.com

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