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Fix the install scheme to `posix_prefix` when `--prefix` is passed

See original GitHub issue

What’s the problem this feature will solve?

On Debian systems, due to the sysconfig patch, sysconfig.get_preferred_scheme('prefix') will return posix_local, which is also the default scheme. This causes problem when using --prefix <path> with pip install, where packages are installed to <prefix_path>/local/lib/pythonX.Y/dist-packages. This is apparently wrong.

Describe the solution you’d like

Add a special case to pip._internal.locations._sysconfig:get_scheme(), when posix_local is found in INSTALL_SCHEMES and prefix is not None, rewrite the scheme as posix_prefix.

Alternative Solutions

I am not sure if it is better to report it to Debian, but IMO it makes more sense to fix it in pip to be more robust.

Additional context

Code of Conduct

I agree to follow the PSF Code of Conduct.

Issue Analytics

State:
Created a year ago
Comments:11 (7 by maintainers)

Top GitHub Comments

2reactions

uranusjrcommented, Mar 22, 2022

Hmm yeah at least they should match. I don’t think Debian can handle this though; the --prefix value is not passed to sysconfig so they have no way to magically choose a scheme based on it. We’ll likely need to somehow handle this in pip, or raise an issue to CPython to further enhance the sysconfig API.

1reaction

pradyunsgcommented, Aug 15, 2022

FWIW, Fedora also has a similarly breaking patch (https://github.com/fedora-python/cpython/blob/f52f499bb9ac03d7793fa2e1ccaaab8a3169685e/Lib/sysconfig.py#L77) and they directly modify posix_prefix.

I suggest we move further discussion to https://discuss.python.org/t/18240, mostly because that’s a better forum for the sort of cross-project discussion that this is gonna need.

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