The short documentation blurb for the -i option says: ignore build-lib and put compiled extensions into the source directory alongside your pure Python modules I tried to write an Extension() where the name of the extension did not match exactly the source directory. Say the extension is called A.B and its source is in src/A/B.c. IOW Extension("A.B", ["src/A/B.c"]) If I run setup.py build_ext -i, then distutils creates an A directory parallel to src and installs A/B.so. That doesn't match the documentation, since it isn't in the same location as the source. Some specific questions about this behavior: Is it intended? If so, then it's a doc bug. Is there a better way to write my setup.py so that I don't run into this behavior directly, e.g. an option to setup() that specifies the source directory (similar to the packages_dir)? Jeremy