--requirements for pip list --outdated

[Jacek Kołodziej]

Hello,

I'm interested in implementing the -r/--requirement argument for pip list --outdated command - see issue https://github.com/pypa/pip/issues/3314 and I have a few questions:

1. At first I treated it as a potential mean to use a requirements file *instead* of list of packages currently installed - but pip list is right now centered around *installed* packages; in this light it's pretty unclear what a --requirement argument should do:

  a) for all installed packages, just add a "wanted" version if installed/wanted versions are below the latest one? or only if installed version is below?

  b) or should it report packages with "wanted" version below the latest one for all packages in the requirements file? what about packages that are there but are not installed?

  c) or should it be an entirely separate mode, disregarding current installation completely, only looking at the requirements file? (which would contradict the very beginning of the pip list description - "List installed packages, including editables.")

2. Whatever the choice, are maintainers even interested in having it implemented? I know *not* having it in the codebase is also a viable way, at least for me, as there is at least one workaround (however much slower) for achieving the same effect as what I'm most interested in - c)

3. Should the answer to 2nd one is "yes": is basing on current master branch a good idea or are there some bigger changes coming to the code that I could miss in present PRs?

If you think the issue thread is a better vehicle for this discussion - just let me know. :)

Kind regards,

Jacek Kołodziej