Specific pip cache location environment variables

[zerothi]

What's the problem this feature will solve?

On HPC systems, or educational systems where a large number of users are using pip to install packages.
For course specific guides, they tend to install the same packages, and thus has a huge number of duplicated cached wheels located in their respective home folders.

Additionally on HPC systems, one will have a backup of the HOME folders which contains the necessary folders. However, backing up a pip cache seems irrelevant (configuring the backup to disable this folder could be done, but annoying).

Describe the solution you'd like

I would like an environment variable that governs the place of the cache (on HPC facilities this could be specified as a default sourced script.

I would propose the name:

PIP_CACHE_HOME

to match the XDG_CACHE_HOME naming convention.

It is clear that XDG_CACHE_HOME is not a good idea to change, since we don't want to alter other programs cache locations.

Alternative Solutions

We have played with the thought of using the /etc/pip.conf for this:

[global]
cache-dir = /glorious/cache

however, it isn't clear how to easily remove a variable using configuration files?

I.e. how can a user disable the cache-dir to just use the XDG_CACHE_HOME variable instead?

[global]
cache-dir = <what to put here to clear it>

Additional context

Nothing to add.

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[notatallshaw]

Does PIP_CACHE_DIR not already work?

[zerothi]

Does PIP_CACHE_DIR not already work?

Ha, I totally missed that option, thanks!!!

Clearly looking in the wrong places of the documentation.

[notatallshaw]

Every pip option in the config (like cache-dir) has an associated environmentable variable as PIP_<UPPER_LONG_NAME>: https://pip.pypa.io/en/stable/topics/configuration/#environment-variables

I would honestly like these all spelt out explicitly in the docs for better SEO, but that's a seperate issue.

[zerothi]

Yes, that top line in that particular section was exactly what I was missing.

I would suggest that section only has:

pip’s command line options can be set with environment variables using the format PIP_<UPPER_LONG_NAME> . 

* Dashes (-) have to be replaced with underscores (_).
* Repeateable options (like ``--verbose``) requires integers as options

with less content it is more likely to see the PIP_<UPPER_LONG_NAME> phrase above. I saw the item list and expected that to contain all available options.

Otherwise just an entry in the list that says PIP_<UPPER_LONG_NAME> would also work, because that clarifies its association with the CMD.

My 2 cents.

Thanks again.

[notatallshaw]

Well, pip is a volunteer project, so doc improvement PRs are usually quite welcome.

[zerothi]

@notatallshaw, done, see #13050.