[Catalog-sig] [Distutils] pre-PEP : Synthesis of previous threads, and irc talks + proposals

[Phillip J. Eby]

At 02:58 PM 10/7/2008 -0400, Tarek Ziadé wrote:
>On Tue, Oct 7, 2008 at 2:42 PM, Phillip J. Eby <pje at telecommunity.com> wrote:
> > At 10:07 AM 10/7/2008 -0400, Tarek Ziadé wrote:
> >>
> >> The -m feature of setuptools is nice, but it activates one version at
> >> a time, and
> >> this is globlal to Python unless each application is handling the
> >> version switch,
> >> wich is pretty heavy.
> >
> > With or without the -m switch, scripts installed by setuptools 
> will find the
> > version they are specified to use, without the user needing to do anything.
> >  So, you can have a default version of an egg (used by the interpreter and
> > non-setuptools scripts), and then some non-default versions that 
> are used by
> > scripts.
> >
> > zc.buildout and virtualenv also have their own ways of accomplishing the
> > same thing, e.g., by hardcoding paths in an installed script.
>
>in a plain python setup,
>
>If foo 1.2 is the default, and a package wants use foo 1.4,
>it needs to specifically call pkg_resources.require() in the code, to
>activate it in sys.path
>before importing "foo" in the code.

You can't un-default the default, actually.  If there's a default, it 
can't be replaced once pkg_resources has been imported.


>Since each package can list with setuptools its dependencies with
>versions in install_requires,
>how hard  would it be to automatically call the right "require()"
>calls when the package is used ?

This is already done by setuptools-generated scripts.  Same for 
zc.buildout and virtualenv, they just do it differently.