sys.prefix should not be used to discover non-dev data directories?

[nazarewk]

Environment

NixOS

Bug description

When packaging ulauncher for Nix (#1307) I noticed it tried to read web app files from within Python installation's directory so I patched it {sys.prefix} -> $out.

Today I started digging into issue and seems like this is a proper behavior according to Python docs:

A string giving the site-specific directory prefix where the platform independent Python files are installed; on Unix, the default is /usr/local. This can be set at build time with the --prefix argument to the configure script. See Installation paths for derived paths.

Note: If a virtual environment is in effect, this value will be changed in site.py to point to the virtual environment. The value for the Python installation will still be available, via base_prefix.

This means sys.prefix does what you want it to do only inside the virtualenv itself (in a development environment?) while:

• ULAUNCHER_DATA_DIR is set up only for development (where it seems not to be needed)
• yesterday's patch does it as a fallback when ULAUNCHER_DATA_DIR is missing, which has no chance of working

Log output

No response

Communication guidelines

• I have read and agree with Ulauncher's communication guidelines and checked the troubleshooting page for self-help.

Not an extension issue

• This issue applies to the Ulauncher application, not a specific extension.

Ulauncher v6

• I have made sure the bug isn't already fixed in v6.

[friday]

This means sys.prefix does what you want it to do only inside the virtualenv itself (in a development environment?)

No. This works perfectly (I'm running it right now and I wouldn't have pushed it if it didn't work). Tested both running from source and installed, Arch and Ubuntu.

How could this only work in a virtual environment when Ulauncher doesn't run in a virtual environment? The documentation says the Unix default is /usr/local for non-virtual environments, but for Arch and Ubuntu it's just /usr

It may be wrong to use sys.prefix here for Nix and/or other OSes though. Both me or the original maintainer have been learning how to handle these things as needed and by trial and error.

[nazarewk]

Makes sense. It assumes ulauncher is installed into that prefix which in itself also makes sense.

The more I think about it the more it seems to be something Nix-specific due to separation of the Python interpreter and per-application packages.

[nazarewk]

Those 2 code pieces seem to be responsible:

• sitecustomization.py
• /bin/* wrapper

[friday]

Yeah, I think the assumptions we have works for traditional package managers where you can only have one version installed of each package. But seemingly not for Nix, and likely not for flatpak (which we should try to support at some point in time).

Maybe you can set the ULAUNCHER_DATA_DIR variable exteranally as a workaround? Or if you need something else, let me know.