Great. If you look closely at the two methods for specifying a pex_binary entry_point described here: https://www.pantsbuild.org/docs/python-package-goal#approach-1-a-file-name https://www.pantsbuild.org/docs/python-package-goal#approach-2-explicit-entry_point You might miss the

python_library()

at the top of the BUILD file. As you found out - that's critical. It's also easy to miss because its not clear why you should need to have it. You might be able to save pain going forward (I still often forget to add a python_library) by using

./pants tailor

. More on that here: https://www.pantsbuild.org/docs/troubleshooting#import-errors-and-missing-dependencies