This is the same bug recently reported by Bob Sidebotham on python-dev (http://mail.python.org/pipermail/python-dev/2007-April/072484.html), but my test-case doesn't involve an overly broad try/except block.

It also seems similar to Bug 1462485, which has been closed and marked fixed, but I can reproduce with my test-case using both python 2.5 and python-trunk (revision 54759).

The irony is that catching the exception to add debugging forces it to be instantiated, thereby avoiding the bug.