This is a simple built-in step that will remove .pyc files from the
workdir. This is useful in builds that update their source (and thus do not
automatically delete .pyc files) but where some part of the build
process is dynamically searching for Python modules. Notably, trial has a bad
habit of finding old test modules.
from buildbot.steps.python_twisted import RemovePYCs
f.addStep(RemovePYCs())