[Distutils] (How) do setuptools/distribute/pip handle circular dependencies?

[Daniel Holth]

The commonest example is that distribute provides setuptools.

Daniel Holth

On Nov 12, 2012, at 6:10 PM, Vinay Sajip <vinay_sajip at yahoo.co.uk> wrote:

> PJ Eby <pje <at> telecommunity.com> writes:
> 
>> Test dependencies allow you to depend on a test framework (e.g. nose) without
>> requiring it to be installed at runtime.  Setup dependencies let you depend
>> on tools like Pyrex or Cython in order to compile a binary package, without
>> requiring them to be available at runtime.
> 
> Oh, I understand why the distinctions exist, and they seem reasonable to me.
> Sorry I wasn't clear - I meant that I wasn't sure how widely these were used. I
> made the comment because I thought that the distinction wasn't preserved in the
> new metadata format, but I must have misread - Daniel commented that the
> distinction *is* preserved.
> 
>> Pkg_resources uses a "greedy" dependency resolver, so it ignores
>> circularity as a side-effect.  That is, as soon as the first requirement for
>> [explanation snipped]
> 
> Thanks for the explanation. It seems to me that the new metadata formats make
> dependency resolution more difficult because they allow for e.g.
> 'Provides-Dist' as a multi-value field. Perhaps I'm misunderstanding, but this,
> it seems to me, opens the door for a project named A on PyPI to provide e.g.
> "A (1.0)", "B (1.5)" and "C (2.0)", and likewise, projects B and C on PyPI
> could provide slightly different versions of "A", "B" and "C". You can soon get
> a rat's nest of dependencies in the resolver - and if you get something like
> the case that Carl linked to, where some element of backtracking might be in
> order, it doesn't seem computationally straightforward to resolve dependencies,
> perhaps even with a SAT solver in the mix. Is this a case of practicality
> losing out to purity? Assuming it's easy to pull any version from an index, I
> can't see a compelling case for any distribution archive for A to ever provide
> anything other than e.g. "A (x.y)". Can someone point me to the real need for
> multi-valued "Provides" fields? Or have I completely misunderstood this aspect
> of the metadata?
> 
> Regards,
> 
> Vinay Sajip
> 
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