Requirements feels like a dirty hack but it does work fine. It has ==, ~=, and >= for version numbers, as well as allowing you to flag dependencies for different target os, etc. And then you can add setup.py if you need custom steps. But yes, it feels dirty to maintain requirements.txt, requirements-dev.txt, etc.

Poetry is the most common solution that I've seen in the wild. You spec everything using pyproject.toml and then "poetry install" and it will manage a venv of its own. But you still need to tell people to "pip install poetry" as step 0 which is annoying.

If you don't care about deploying python files, and rather just the final product, I'd recommend either nuitka or pyinstaller. These are for bundling your project into an executable without a python runtime needed (--onefile type of options for single file output). Neither supports cross compilation though.