During Py_Finalize (pythonrun.c), it does the following:
1) suppress signal handling PyOs_FiniInterupts
2) clear caches
3) force gc collection; first for objects, then via wiping modules.

The problem is that for unix OSs, Modules/signal.c's PyOs_FiniInterrupts leaves itself in a state where its internal Handlers are effectively reset to NULL, except the various functions don't properly handle that scenario.

Attached is a test case demonstrating it; it segfaults on every python version I've tested (2.4->3.2; haven't tried 3.3).

Since this *only* occurs during the final gc sweep when modules are destroyed, its a bit of a pain in the ass to detect that we're in that scenario, and that we must not touch signal.getsignal lest it segfault the interp.  That said,

def _SignalModuleUsable():
try:
  signal.signal(signal.SIGUSR1, signal.signal(signal.SIGUSR1, some_handler))
  return True
except (TypeError, AttributeError, SystemError):
  # we were invoked in a module cleanup context.
  return False

does manage to poke the api just right so that it can be detected w/out segfaulting the interp.

Finally, note that while folks could point at __del__... its not really at fault.  Doing a proper weakref.ref finalizer can trigger the same- the fault is signal.c's PyOs_FiniInterrupts leaving the signal module in a bad state.  For the testcase, I used __del__ just because it was quicker/less code to do so.

I needed to modify the script to make it crash under 3.2/3.3. Attaching modified version.

Here is the relevant part of the gdb traceback:

Program received signal SIGSEGV, Segmentation fault.
0x000000000052b87b in signal_getsignal (self=<module at remote 0x7ffff7f43a38>, args=(1,))
    at ./Modules/signalmodule.c:372
372	    Py_INCREF(old_handler);
Missing debug package(s), you should install: glibc-debug-2.12.1-11.3.mga1.x86_64
(gdb) bt
#0  0x000000000052b87b in signal_getsignal (self=<module at remote 0x7ffff7f43a38>, args=(1,))
    at ./Modules/signalmodule.c:372
#1  0x00000000005f520b in PyCFunction_Call (func=
    <built-in method getsignal of module object at remote 0x7ffff7f43a38>, arg=(1,), kw=0x0)
    at Objects/methodobject.c:81

New changeset 0201d8fa8bd0 by Antoine Pitrou in branch '2.7':
Issue #14173: Avoid crashing when reading a signal handler during interpreter shutdown.
http://hg.python.org/cpython/rev/0201d8fa8bd0

New changeset 0dfd5c7d953d by Antoine Pitrou in branch '3.3':
Issue #14173: Avoid crashing when reading a signal handler during interpreter shutdown.
http://hg.python.org/cpython/rev/0dfd5c7d953d

New changeset 753bcce45854 by Antoine Pitrou in branch 'default':
Issue #14173: Avoid crashing when reading a signal handler during interpreter shutdown.
http://hg.python.org/cpython/rev/753bcce45854

This should be fixed now. Thank you for diagnosing this bug!