Understanding multiple targets USE Expand

[SDD701]

Hi. Can anyone explain what exacly is PYTHON_TARGETS actually mean? As far as I get it I can launch a program using marked versions. For example if I emerge qtile with -python3_10 python3_11 python3_12 I can start it using python 11 and 12 but not 10. Is that correct? How can I switch versions?

[grknight]

Any executable python script installed with PYTHON_TARGETS set will be put behind python-exec2 (from dev-lang/python-exec) which figures out what version to call.

python-exec2 determines what version to run through a few factors in this order:

• First, if the EPYTHON environment variable is set, use that to determine which version to start.
  
• Next, if /etc/python-exec/$command.conf exists (where $command is what is called in the shell), use that file to determine which version to start.
  
• Finally, use the generic settings of /etc/python-exec/python-exec.conf defaults to determine what version to start. (In modern times, this should be controlled by dev-lang/python-exec-conf unless there's a good reason)

All of the above is considered for validity of supported version strings and availability by what the script was installed with. Each step falls through until a valid configuration is found or just flat out fails.

Using the example provided, EPYTHON="python3.11" qtile would be run under python 3.11 exclusively.

Packages which provide libraries for other python modules often need PYTHON_TARGETS to ensure multiple versions are available.

For simple scripts, it is more advantageous to consider using PYTHON_SINGLE_TARGET instead particularly for leaf packages. This only allows for a single version and is installed directly with its bangpath fixed.

[SDD701]

Thank you, now I understand the concept

[logrusx]

Some more explanations:

https://projects.gentoo.org/python/guide/eclass.html#single-impl-vs-multi-impl

Best Regards,
Georgi