When a second potential .py file is considered, setuptools plays better with src/

I've found it difficult in #38 to get the entrypoints and multiple modules in a flat structure to work correctly. It seems by design it doesn't work (or else people would be committing junk [1]):

If you are using auto-discovery with flat-layout, setuptools will refuse to create distribution archives with multiple top-level packages or modules.

This is done to prevent common errors such as accidentally publishing code not meant for distribution (e.g. maintenance-related scripts).

Users that purposefully want to create multi-package distributions are advised to use Custom discovery or the src-layout.