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

[Daniel Holth]

On Mon, Nov 12, 2012 at 3:39 PM, PJ Eby <pje at telecommunity.com> wrote:

> On Sat, Nov 10, 2012 at 6:51 AM, Vinay Sajip <vinay_sajip at yahoo.co.uk>wrote:
>
>> Carl Meyer <carl <at> oddbird.net> writes:
>>
>> > already satisfied. In pip this happens here:
>> > https://github.com/pypa/pip/blob/develop/pip/req.py#L1091
>> >
>> > More generally, I wouldn't really recommend pip's dependency resolution
>> > logic as a model for new Python code in this area. There are some not
>> > uncommon cases that it handles poorly; see
>> > https://github.com/pypa/pip/issues/174 and
>> > http://bugs.python.org/issue8927. (To be fair to pip, these cases
>> aren't
>> > trivial when you have to download and unpack an sdist before you can
>>
>> Thanks for the pointers.
>>
>> > find out anything about its dependencies, but I'd hope that with the new
>> > metadata PEPs Python packaging code could get a bit smarter in this
>> area.)
>>
>> AFAICT, the proposed metadata PEP changes don't offer the same requirement
>> granularity as setuptools / distribute (for example, 'Requires-Dist' as
>> against
>> 'install_requires', 'setup_requires', 'test_requires').
>>
>> Anyway, I'll take a look at the issue you mentioned and see how the
>> dependency
>> code in distlib stacks up. Currently, it keeps the requirements distinct
>> for
>> 'install', 'setup' and 'test'. The distinctions seem reasonable in theory,
>> though I'm not sure how useful they are in practice.
>>
>
> 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.
>

I'm not sure this is well understood, let's make sure everyone gets this.

With setup/test requirements as implemented in setuptools nose, Pyrex,
Cython, whatever can be on PYTHONPATH during the install but are not
available when the install is done. You get to use them without cluttering
up your normal runtime environment. This is implemented by installing nose
in a uniquely named subdirectory of the sdist that is being installed and
adding that directory to PYTHONPATH/sys.path during the install / test
command run.


I would like to see distutils (1, 2, any number) banished from the stdlib
to become a common setup-requires requirement.
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