Update dependency management docs

[abravalheri]

Summary of changes

• Extract depencency_liks section to a new file:
  deprecated/dependency_links.rst
• Add note about directly URLs not being accepted in PyPI.
• Simplify intro about build system requirement.
• Simplify intro about optional dependencies.
• Fix confusion in example about "Project" and "Package".
• "Demote" section about extras in entry-points to a note.

Pull Request Checklist

• Changes have tests
• News fragment added in changelog.d/.
  (See documentation for details)

[dkondoetsy]

@abravalheri thanks for this PR. Now that dependency_links is deprecated, is there an alternative way to specify a different non-pypi package index url [eg in artifactory/jfrog] to setuptools.setup()?

I've tried the install_requires argument to setuptools.setup() like so:

install_requires=[mypackage @ http://USER:PASSWORD@myhostname:8082/api/pypi/pypi/simple]

but install_requires seems to expect to download source code as a [.zip] archive.

Ideally, I'm looking for something equivalent to pip's extra-index-url setting, which is specifiable directly to setuptools.setup().

[abravalheri]

Hi @dkondoetsy, I couldn't find anything in the latest packaging standards about mixing multiple package indexes together directly on the package specification. You need to use an external tool for that, like the pip configuration file, or a package index mirror/proxy like devpi (maybe bandersnatch also can do that?).

What is possible to do right now is to force a URL to a wheel file as covered in PEP 440/PEP 508. But as you have already noticed, it requires you to point to a specific file and don't allow for dynamic version resolution.

So the short answer is no, unfortunately there seems to be nothing in the packaging standards regarding that.

[dkondoetsy]

Thank you very much, @abravalheri, for your response and the other options you listed.

I will look into pointing to a wheel and appreciated the documentation you pointed to PEP 440.