To further elaborate on 2, it solves the problem of maintaining loose version ranges in your requirements.txt file, but keeping the versions pinned when you deploy. For example if you put `foo>=2` in your requirements.txt, this is dangerous without some way of pinning e.g. `foo==2.18.2` and running your tests against that before you deploy. But you obviously don't want to manually edit requirements.txt with minor version numbers every time you update. In the past I've maintained a separate file with loose versions and then updated packages with
pip install -r requirements-to-freeze.txt --upgrade && pip freeze -l -r requirements-to-freeze.txt > requirements.txt