You weren't kidding at all.
After spending more time than I'd care to admit searching for the library, I couldn't find traces of it anywhere on google, ddg, or bing. I relented and digged whatever information I could find in my history.
Revisiting these projects, it's painfully obvious that I have jumbled a few projects together. Sincere apologies for the unintended goose chase.
This project [1] is the one that introduced the `--_completion` flag. It registers itself as a default completion function, but blindly and dangerously tries to run any command it gets with this flag. (This project is completely de-indexed from search engines and I'm not sure why).
Like [1], project [2] registers itself as a default completion function, but checks the first 1024 bytes for the magic string "PYTHON_ARGCOMPLETE_OK". It seems to be relying on argparse for completion.
I couldn't manage to find the project that was scanning elf sections. I'm not entirely sure if it was relying on elf sections specifically or if the fact that it was scanning elf sections was only an implementation detail.
[1]: https://github.com/dbarnett/python-selfcompletion [2]: https://github.com/kislyuk/argcomplete
I'm interested to know more about that ELF / --_complete trick though. Do you have any more details? (when DDging the only result I can find on the topic is your comment)