In setuptools.command.bdist_egg:write_stub() Setuptools writes this function out alongside .so files: def __bootstrap__(): global __bootstrap__, __loader__, __file__ import sys, pkg_resources, imp __file__ = pkg_resources.resource_filename(__name__,<resource filename>) del __bootstrap__, __loader__ imp.load_dynamic(__name__,__file__) __bootstrap__() This is problematic on App Engine, as the .py file is loaded because .so files cannot be imported. However, unlike a zip file (where I assume this function is intended to be used) there is no __loader__. As a result "del __loader__" fails. I submitted this to App Engine (http://code.google.com/p/googleappengine/issues/detail?id=229), but I also think Setuptools is creating an unnecessarily fragile function here. -- Ian Bicking : ianb@colorstudy.com : http://blog.ianbicking.org