python-exec (c) 2012-2018 Michał Górny Licensed under the terms of the 2-clause BSD license.
python-exec is a wrapper for Python scripts and executables designed in order to facilitate the support for installing multiple Python implementations in parallel.
python-exec provides support for wrapping Python implementations whose identifiers (executable basenames) are passed during configure call (obligatory --with-python-impls parameter).
In order for python-exec to work, wrapped scripts and executables need to be installed in subdirectories of scriptroot (defined through --with-python-scriptroot parameter, ${prefix}/lib/python-exec by default) whose names match appropriate implementations. Afterwards, python-exec2 wrapper should be symlinked or copied into an appropriate executable directory using the name of the wrapped script.
In other words, to wrap /usr/bin/foo, you would:
install the real script into /usr/lib/python-exec/pythonX.Y/foo,
symlink /usr/bin/foo -> /usr/lib/python-exec/python-exec2.
Afterwards, whenever the wrapper script is run python-exec will try to determine the most preferred Python implementation supported by the script and run the appropriate variant. It should be noted that the wrapped script needs to have an appropriate shebang in order to run matching Python interpreter.
python-exec supports two configuration layers: EPYTHON environment variable and a configuration file.
The EPYTHON environment variable can be used to configure python-exec at runtime and/or override local configuration. If it is defined, it specifies the most preferred Python interpreter that should be used to run the script. If the specified interpreter is unsupported by the script, python-exec will fall back to configuration file and/or default order.
The configuration file (example in config/python-exec.conf.example) needs to be installed in ${sysconfdir}/python-exec/python-exec.conf. It lists preferred Python implementations in preference order. For more information, please look at the detailed usage guide in the example file.
If none of the explicitly preferred implementations are supported by the script, python-exec falls back to trying any other implementation known to it (i.e. specified at build-time) that is not explicitly disabled via configuration.
python-exec2 itself and its build system does not require any version of Python being installed. This also means that it can be securely reinstalled if it becomes broken and Python scripts stop to work correctly.
If the python-exec2 wrapper (in ${python_scriptroot}) becomes damaged (e.g. overwritten by insecure use of old version of distutils), you can replace it with python-exec2c wrapper (from ${bindir}). This will break uses of 'python /usr/bin/foo' but otherwise render the wrapper functional.
The python-exec2c wrapper can be called directly. For example, in order to execute the script foo, you can call:
python-exec2c fooAll wrapped scripts are installed in ${python_scriptroot} and usable directly. If everything else fails, you can simply call:
/usr/lib/python-exec/python3.4/foo