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During installation of Python packages (setup.py install or bdist), distutils puts .pyc files into the installed source directory, instead of moving them into __pycache__. This may mean that they are not getting used after installation (with potentially no way of getting updated due to lack of write access by users), and that source files that get imported during installation may end up with .pyc files in both the source directory and the __pycache__ directory in the installed package.
The relevant python-dev thread is here:
http://thread.gmane.org/gmane.comp.python.devel/121248/ 

Here's a patch. I basically copied over the way py_compile determines the .pyc file name.
It works for me for a "normal" installation. However, I couldn't test it with "-O", as 2to3 crashes for me when I enable it during installation. I guess that's a separate issue.

Patch looks good. Regarding the problem with 2to3 and -O, maybe you can run 2to3 manually, copy the setup.py and run python3.2 -0. disutils.util.byte_compile is not tested, so this patch requires at least careful manual testing, and if possible a unit test.
In distutils2, it may be possible to replace this function with a compileall call.

This patch applies cleanly as of rev 89af3880ca57 on branch default.
After applying the patch, I had two unit test failures when running,
"/python.exe -m test -v test_distutils", on OS X 10.6. The tests were failing because they were not looking in the __pycache__ directory for byte-compiled or optimized files.
Attaching an updated patch that fixes the unit tests that were breaking.

Thanks for the test. The patch is minimal and makes distutils work correctly with the new pyc handling in 3.2+, so I will apply it in a few days unless Tarek disagrees.

I cleaned up the patch a bit. In particular, I removed the dance around imp.cache_from_source that seemed unnecessary. I tested with regular Python, with PYTHONOPTIMIZE and with PYTHONDONTWRITEBYTECODE. Can you review and test too?

The dance around imp.cache_from_source looks necessary, judging by Georg’s http://hg.python.org/cpython/rev/713c6b6ca5ce/#l8.53 

I've reviewed your patch and it looks good. I appreciate the review and cleanup.
The tests succeed for me after applying your patch. I also tested with PYTHONOPTIMIZE and PYTHONDONTWRITEBYTECODE and got the output I expected.

Should this be a release blocker for 3.2.1?

to be backported in packaging -- in a way that will make it work with previous python versions for the incoming 2.x backport

FWIW, I've filed a bug about this issue for Fedora 15's python3 package here: https://bugzilla.redhat.com/show_bug.cgi?id=722578
Looks like this has led to an extra .pyc in the old location for every Python 3 .py file in Fedora 15's various python3-* rpm packages (as generated by distutils). 
rpm's post-processing has been generating .pyc files in the (correct) __pycache__ location (via rpmbuild's brp-python-bytecompile script, which uses "compileall").
For examples, see that Fedora bug report; so far it's affected every built rpm I've looked at.
I believe the impact of the extra .pyc files is merely wasted disk space within our rpm-packaged Python 3.2 stack.
I'm thinking of applying the patch to our downstream python3.src.rpm

I will commit this today or tomorrow.

New changeset 27a36b05caed by Éric Araujo in branch '3.2':
Fix distutils byte-compilation to comply with PEP 3147 (#11254).
http://hg.python.org/cpython/rev/27a36b05caed
New changeset 651e84363001 by Éric Araujo in branch '3.2':
Fix docstring of distutils.util.byte_compile (followup for #11254)
http://hg.python.org/cpython/rev/651e84363001
New changeset 439f47fadffa by Éric Araujo in branch 'default':
Fix packaging byte-compilation to comply with PEP 3147 (#11254).
http://hg.python.org/cpython/rev/439f47fadffa 

Finally fixed. I fail at boolean logic; removing the "dance around imp.cache_from_source that seemed unnecessary" as I called it was a mistake, we have to do it, so I restored that part of your original patch. I’m sorry I took so long to fix this, it was straightforward.

New changeset 1cc4d822123b by Éric Araujo in branch 'default':
More fixes for PEP 3147 compliance in packaging (#11254)
http://hg.python.org/cpython/rev/1cc4d822123b 

Installation was not completely fixed. Distutils delegates to each command’s get_outputs method to make the list of all files to install or package in an sdist, and the previous patch missed edits to these get_outputs methods. I should have fixed it in packaging, I’ll port to distutils soon.

New changeset ea926dff958f by Éric Araujo in branch '3.2':
More fixes for PEP 3147 compliance in distutils (#11254)
http://hg.python.org/cpython/rev/ea926dff958f
New changeset 60ede940089f by Éric Araujo in branch 'default':
Merge follow-up for #11254 and other changes from 3.2
http://hg.python.org/cpython/rev/60ede940089f 

New changeset c10946a17420 by Éric Araujo in branch 'default':
Clean up byte-compilation code in packaging (#11254 followup).
http://hg.python.org/cpython/rev/c10946a17420 

See also #13123 for the same bug in bdist_wininst.