[Python-porting] Python 2/3 compatible distutils installation?

[Barry Warsaw]

Here's an interesting porting issue that came up today.  I'm not crossposting
this to distutils-sig, but I will if no one here has come up with a solution.

I'm looking at testtools[1], which Jerry Seutter has done a good, initial port
of to Python 3.  His merge proposal, along with the diff is here[2].  My
branch which fixes a few of Robert Collins' comments is here[3].

One of the tricky problems is with re-raise syntax, which can't be
compatibly represented syntactically across Python 2 and 3.  The six module
has a hack for this, but testtools uses its own trick, which is to provide a
_compat2x.py and a _compat3x.py file containing the proper syntax.

This works well at execution time, because a simple sys.version_info check can
be used to decide which module gets imported; the other is for all intents and
purposes, ignored.

The problem comes when installing the package with distutils.  The
byte-compilation of _compat2x.py throws a SyntaxError, of course rightly so.

The question I have is how can we avoid trying to byte compile _compat2x.py
when the package is installed via Python 3?  I've tried various distutils
command overrides and hacks (including trying to load a MANIFEST3.in which
exclusions that file), but haven't hit upon the right magic to make it work in
all cases.

Has anybody encountered a similar situation, and if so, how have you worked
around this?  Disgusting kludges welcome. :)

Cheers,
-Barry

[1] http://launchpad.net/testtools
[2] https://code.launchpad.net/~jseutter/testtools/py3_again/+merge/105569
[3] https://code.launchpad.net/~barry/testtools/py3
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