The project has a Makefile that does not reinstall dependencies repeatedly. Additionally, it utilizes Python tox to run tests in various Python environments automatically. However, your current demonstration involves creating a Python build from scratch, despite the availability of several project templates.
If you operate in a virtual setting, why manually generate requirements.txt when you can automate the process?
pip freeze > requirements.txt
The information provided in this link (which may be a duplicate) clarifies the topic.