[gentoo-dev] Versioning of Python scripts

[Arfrever Frehtes Taifersar Arahesis]

Distutils/Setuptools/Distribute modify shebangs of installed Python scripts, so that they
contain path of Python interpreter with version included (e.g. "#!/usr/bin/python3.2").
This behavior has both advantage and disadvantages:
  - Scripts of packages supporting only e.g. Python 2 can be executed (without necessity
    of using of e.g. "python2 /usr/bin/${script}") after activating of e.g. Python 3.
  - Scripts of packages supporting multiple Python versions ignore active Python version.
  - Scripts of packages supporting multiple Python versions cannot be easily (without
    necessity of using of e.g. "python3.1 /usr/bin/${script}") executed with a Python
    version different than active Python version.
The best solution, which removes these 2 disadvantages and preserves the advantage, seems
to be to rename Python scripts to include Python version [1] in filenames, and create wrapper
scripts, which call appropriate target scripts [2]. Some files sometimes try to execute
e.g. "/usr/bin/python /usr/bin/${script}", so wrapper scripts must be implemented in Python.
Wrapper scripts try to execute "${wrapper_script}-${PYTHON_ABI}" files (e.g. "py.test" will
execute "py.test-3.1", when Python 3.1 is set as active Python version).

distutils.eclass will automatically rename some scripts [3] in "${D}usr/bin" and call
the function, which generates wrapper scripts. In case somebody is interested in reading of
source code of python_generate_wrapper_scripts() function and potential suggesting of
improvements, I'm attaching this function and 2 example wrapper scripts. I'm planning to
commit addition of this function in next week.

[1] Actually Python ABI.
[2] Wrapper scripts can also be created for ELF target files (e.g. "mpipython").
[3] Only scripts of packages supporting installation for multiple Python versions will be
    renamed. Scripts, whose filenames end in [[:digit:]]+\.[[:digit:]]+, won't be renamed.

-- 
Arfrever Frehtes Taifersar Arahesis