Title: PYTHON_TARGETS deployment
Author: Michał Górny <mgorny@gentoo.org>
Content-Type: text/plain
Posted: 2012-11-06
Revision: 1
News-Item-Format: 1.0

Recently, a few new Python eclasses have been deployed. As ebuilds
migrate, the way they support multiple Python implementations will
change. The previous method built Python modules for Python
implementations selected through `eselect python'. The new method uses
the PYTHON_TARGETS USE flags to explicitly name the implementations the
modules shall be built for.

If you are running a modern system with only Python 2.7 & 3.2 installed,
then you don't have to do anything. The defaults will simply fit you,
and let you keep your system up-to-date when new Python versions are
deployed.

However, if you'd like to use another set of Python implementations, you
will need to set PYTHON_TARGETS in your make.conf file appropriately.
This variable names the enabled implementations in the standard way
common to all USE_EXPAND variables.

For example, a setup enabling all major Python implementations would
look like:

	PYTHON_TARGETS="python2_7 python3_2 pypy1_9 jython2_5"

The variable should list all Python implementations which are going to
be used on the system; missing a particular value there will result
in missing Python modules.

A complete list of all possible values can be obtained using a command
equivalent to the following:

	emerge -1pv dev-python/python-exec

For more details, please see the python-r1 User's Guide [1].

[1] http://www.gentoo.org/proj/en/Python/python-r1/user-guide.xml