Recently, after a small seemingly unrelated refactoring, the SymPy test suite in Python 3 started dying with "Fatal Python error: Cannot recover from stack overflow."  

Here's how to reproduce the error

git clone git://github.com/sympy/sympy.git # Clone the development version of SymPy
cd sympy
git checkout 0856119bd7399a416c21e1692855a1077164f21c # This is the first commit to exhibit the problem. Do this in case we make an unrelated change that removes the problem.
./bin/use2to3 # Convert the codebase to Python 3
python3 py3k-sympy/setup.py test # Run the tests

The issue is described in more detail at http://groups.google.com/group/sympy/browse_thread/thread/f664fe88e6b4f29d/3a44691c945695db#3a44691c945695db.  Some key points:

- The test that triggers the error is an XFAIL test (test that is expected to fail) that raises RuntimeError: maximum recursion depth exceeded.

- The change that caused the error, 0856119bd7399a416c21e1692855a1077164f21c (see https://github.com/sympy/sympy/commit/0856119bd7399a416c21e1692855a1077164f21c), is seemingly unrelated.  The only thing that I can think of is that it has added another call to the stack.

- This kills Python with Abort Trap: 6 in Mac OS X, which generates a problem report to be sent to Apple.  I have included a copy of it here: https://gist.github.com/2317869.

- Others have reproduced this error as well, as can be seen by our test reporter tool.  See the mailing list thread for more info.

- I tested this in 3.2.3r2, and the error still occurred.  I tried testing in the 3.3 alpha, but I could not get it to compile.