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

[Daniel Holth]

It is an error to refer to an extra that has not been declared. In
your case you would get an error if some version of Django >= 1.4 that
did not declare the extra was installed.

pip install pip[pop]
  UnknownExtra: pip 6.0.6 has no such extra feature 'pop'

One thing you could do with the current technology is to have two
empty mezzanine-django-old and mezzanine-django-new packages that just
depend on a third mezzanine package, the appropriate version of
django, and the appropriate comments add on.


On Thu, Jan 22, 2015 at 1:18 AM, Alexander Hill <alex at hill.net.au> wrote:
> 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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