MANIFEST.in ignored on "python setup.py install" - no data files installed?

MANIFEST.in tells Distutils what files to include in the source distribution but it does not directly affect what files are installed. For that you need to include the appropriate files in the setup.py file, generally either as package data or as additional files.

I couldn't figure out why my MANIFEST.in file was being ignored when I ran python setup.py install - turns out include_package_data=True solves the problem. The package_data option isn't actually required.