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In bz2.py, "import threading" prevents the bz2 module from working when threads are not enabled. The attached patch removes the limitation and provides a fake lock object.
I don't know if this should be backported to 3.2.

Isn't there already a dummy lock in dummy_threading?

As Georg suggested, it would be better to use dummy_threading.RLock,
rather than providing our own implementation.
The test in the patch fails when I try to run it on a no-thread build.
support.import_fresh_module seems to treat the absence of the threading
module as an error, and returns None instead of allowing the bz2 module
to recover from the ImportError.
We needn't worry about 3.2. It still uses the old all-C implementation,
which has its threading dependencies protected by #ifdefs.

New changeset 2fb93282887a by Nadeem Vawda in branch 'default':
Issue #13809: Make bz2 module work with threads disabled.
http://hg.python.org/cpython/rev/2fb93282887a 

Fix committed. For the test, it turns out we can get the desired behavior
by telling import_fresh_module to block the threading module directly,
instead of blocking _thread.