...because otherwise it is impossible to upgrade from python:3.2 to python:3.3 on a "FEATURES=test"-enabled system.
Reasoning: test-enabled systems need to resolve the circular dependency between dev-python/py and dev-python/pytest, for each update, via "FEATURES=-test emerge -v1 dev-python/py && emerge -v1 dev-python/py dev-python/pytest"
Now, in order to upgrade from python:3.2 to python:3.3, the above step has to be done, building exactly these two packages. In order to be able to do so, dev-python/setuptools needs to be build with the new python3_3 target -- but at the same time, it still has to provide the old python3_2 target for all the other packages which will be updated *after* resolving the circular dependency. Thus, for the time of the upgrade, dev-python/setuptools has to be rebuild first with both python targets (plus python2_7, if required), then all the update/rebuilds take place, then finally dev-python/setuptools can be rebuilt without the python3_2 target. (Or at least that's the most sane way I have come up with so far.)
After the masking of python3_2 on September 6th, this has become (afaik) impossible without rebuilding major parts of the system with tests disabled just to make "emerge world" happy with all the dependencies, *or* emerge with --nodeps which also isn't really helpful for having stable systems.
*** This bug has been marked as a duplicate of bug 516550 ***
Author: Justin Lecher <email@example.com>
Date: Mon Nov 23 10:42:05 2015 +0100
dev-python/setuptools: Drop old
Signed-off-by: Justin Lecher <firstname.lastname@example.org>