It has only recently sunk in for me that, with the latest versions, Pip is not a tool for maintaining an environment and list of dependencies (where you'd have

It has only recently sunk in for me that, with the latest versions, Pip is not a tool for maintaining an environment and list of dependencies (where you'd have a lockfile, for example). Instead, it is an interface to… 1. Download packages from PyPi (or a different repository that provides the same interface) 2. Read the pyproject.toml file to find the build backend to use, and then install that. 3. Call the build backend to actually do the installation. This can be Poetry, Setuptools, Flit, or something else. Pipenv is another such interface. PEP 517 (https://peps.python.org/pep-0517/ https://peps.python.org/pep-0517/) created pyproject.toml and defined the API that build backends follow. That API includes a way for the build backend to tell Pip (or Pipenv, etc.) what dependencies to install. For systems that have a lockfile (like Pipenv), that could be a list of packages with explicit versions. PIP 660 extended PEP 517, defining a standard way to have "editable installs". In other words, a way to support `pip install -e package`, or even `pip install -e .`. The above is all my understanding, which is not at all authoritative! It's worth checking out the list of packaging-related PEPs: https://peps.python.org/topic/packaging/ https://peps.python.org/topic/packaging/ It's worth reading PEPs 518 and 621. As an example, here's a Python package that uses Poetry: https://github.com/globus/globus-timer-cli https://github.com/globus/globus-timer-cli It works perfectly fine with Pip, because Pip sees (via `pyproject.toml`) that it needs to pull in Poetry, and call it to do the actual install. Here's an older repo of mine, where I've just started to learn about the transition: https://github.com/stanford-rc/mais-apis-python/blob/main/pyproject.toml https://github.com/stanford-rc/mais-apis-python/blob/main/py... In this case, I could delete `pyproject.toml` entirely, Pip would see the `setup.py` file, and understand to use Setuptools. This was me when I was just starting to learn about the transition. Finally, here's a newer repo of mine, where I've ditched setup.py (and _almost_ ditched setup.cfg) entirely: https://github.com/stanford-rc/globus-group-manager https://github.com/stanford-rc/globus-group-manager I'm still using Setuptools, but all of the metadata and requirements are included in the `pyproject.toml` file. It's definitely been a rocky transition, but it's really looking (to me, at least) like we're at (or near) the point where I can just use `pip install …` and it'll work, regardless of the build backend in use!