[Distutils] Dependencies conditional on specific installed versions of other dependencies?

[Alexander Hill]

Hi Nick,

Just thinking some more about the scenario where Django defines a
"comments" extra.

Say in our setup.py we have install_requires=['django[comments] >= 1.4'].
What happens when this setup.py is run with Django 1.4 already installed?
Is the (missing) extra just ignored, or will Django be upgraded to a
version which declares the extra?

(anyone following along, please see my response to Nick below - forgot to
reply all)

Cheers
Alex

On Thu, Jan 22, 2015 at 2:04 PM, Alexander Hill <alex at hill.net.au> wrote:

> Thanks for your feedback Nick.
>
> Just checking my understanding: say default extras existed and we'd
> implemented them as described, and I'm a Mezzanine user running Django 1.4.
> I see a new version has been released, don't read the release notes
> thoroughly, and run pip install --upgrade mezzanine as usual instead of
> specifying [-comments]. This would still install django-contrib-comments
> and upgrade Django in the process, is that right?
>
> Seems like the cleanest way to do this would be for Django itself to
> define a "comments" extra, requiring django-contrib-comments, in Django
> 1.8's setup.py.
>
> Cheers,
> Alex
>
> On Thu, Jan 22, 2015 at 1:29 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:
>
>> On 21 January 2015 at 16:13, Alexander Hill <alex at hill.net.au> wrote:
>> > Hi all,
>> >
>> > I have run into a bit of a head-scratcher.
>> >
>> > Prior to the upcoming version 1.8, Django included a comments app at
>> > django.contrib.comments. As of 1.8, the app has been broken out into an
>> > independent package, django-contrib-comments [1].
>> django-contrib-comments
>> > requires Django >= 1.5.
>> >
>> > The project I'm working on (Mezzanine) requires Django comments. I want
>> > Mezzanine to support Django 1.4 through to 1.8, so I need
>> > django-contrib-comments. But because it requires Django >= 1.5, when
>> it's in
>> > my dependencies Django gets automatically upgraded if version 1.4 is
>> > installed, so the Mezzanine test suite isn't actually run under 1.4 [2].
>> >
>> > Is there some way to only depend on django-contrib-comments if a minimum
>> > version of Django is installed? Or any other way around this problem?
>> Any
>> > advice greatly appreciated!
>>
>> The closest I can think of is to make the comments support an extra,
>> so you'd need to specify "mezzanine[comments]" to get
>> django-contrib-comments on 1.5+. That's unlikely to be acceptable in
>> this case though, since existing dependencies on mezzanine would fail
>> to install the comments support.
>>
>> While it won't help you right now, I did have an idea for a possible
>> way to deal with this in PEP 426: provide a way to specify a set of
>> "default extras" for a project. Those dependencies would still be
>> installed by default, but you'd have an easy way to turn them off if
>> you didn't want them.
>>
>> Then, in this case, you'd be able to run the Django 1.4 tests using
>> "mezzanine[-comments]" rather than a default install to avoid
>> attempting to install django-contrib-comments.
>>
>> Filed as: https://github.com/pypa/interoperability-peps/issues/18
>>
>> Regards,
>> Nick.
>>
>> --
>> Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
>>
>
>
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