I think I've found a bug in the site.py of 3.1.2. The following piece of code tries to make the modules that are normally installed under lib-dynload available when running from the build directory: """Append ./build/lib.<platform> in case we're running in the build dir (especially for Guido :-)""" from distutils.util import get_platform s = "build/lib.%s-%.3s" % (get_platform(), sys.version) if hasattr(sys, 'gettotalrefcount'): s += '-pydebug' s = os.path.join(os.path.dirname(sys.path[-1]), s) sys.path.append(s) However, it doesn't always work, because distutils.util.get_platform tries to find a Makefile in the install location, which doesn't exist if the Python you're building has never been installed! -- Greg