This is a record of analysis and consequent workaround to enable running ipython and Twisted's trial. Posting to twisted, it probably requires no action from twisted team since I suspect IPython is not dealing with the situation correctly. Ipython needs to resolve the problem w/ a try: import thread except ImportException: print "failed to import thread" import dummy_thread as thread For ipython to 'work' I copy dummy_thread.py thread.py, then when I run trial or twistd I see the following exception. If I delete the thread.py this does not show up, but ipython stops working. Exception exceptions.ImportError: 'No module named threading' in <bound method local.__del__ of <_threading_local.local object at 0xb72f6874>> ignored (venv)[miwinter@sawwing test]$ twistd -ny finger.tac shows the same exception (from twisted's finger tutorial). Python -V 2.4.5 and 2.5.1 and 2.5.2 Ipython-0.8.2 * Twisted 8.1.0 virtualenv 1.0 CVSToys 1.0.10 python -m virtualenv venv . venv/bin/activate (venv)# make InstallTwisted (cd Twisted-8.1.0; python setup.py install) (venv)# make InstallBuildbot (easy_install buildbot) (venv)# trial buildbot.test.test_twisted .... Shows the above problem: [skip] PASSED (skips=37, successes=271) Exception exceptions.AttributeError: "'NoneType' object has no attribute 'StringIO'" in <bound method RemoteReference.__del__ of <twisted.spread.pb.RemoteReference instance at 0xb6856aec>> ignored Exception exceptions.ImportError: 'No module named threading' in <bound method local.__del__ of <_threading_local.local object at 0xb72dacfc>> ignored test main-trunk]$ md5sum lib/python2.4/thread*py lib/python2.4/dummy_thread*py 3783492a0969521ff1266ec6c3e570c2 lib/python2.4/threading.py 38db2323ac32ddbcad69888abd30d21f lib/python2.4/dummy_threading.py 52a6d92c98cc5a2eb68a3b1dde16e58b lib/python2.4/thread.py 52a6d92c98cc5a2eb68a3b1dde16e58b lib/python2.4/dummy_thread.py Without thread.py ipython will fail to start, so in my makefile I do: fixThread: bin/python lib/python$(PY_MACRO_VERSION)/thread.py lib/python$(PY_MACRO_VERSION)/thread.py: (cd lib/python$(PY_MACRO_VERSION); cp dummy_thread.py thread.py) This exception (see start of email) is perhaps caused by dummy.py lacking some of the guts that some inappropriately intimate part of threading.py depends upon. w/o target fixThread ipython will not start! Since resolving this by bandaiding Makefile I thought it worthy to report that my patch to my Makefile was to add target unfixThread: to reverse the effects of fixThread which was a hack for ipython to work, better fix ipython somehow.