python - What is pyproject.toml file for?

Question

Background

I was about to try Python package downloaded from GitHub, and realized that it did not have a setup.py, so I could not install it with

pip install -e <folder>

Instead, the package had a pyproject.toml file which seems to have very similar entries as the setup.py usually has.

What I found

Googling lead me into PEP-518 and it gives some critique to setup.py in Rationale section. However, it does not clearly tell that usage of setup.py should be avoided, or that pyproject.toml would as such completely replace setup.py.

Questions

Is the pyproject.toml something that is used to replace setup.py? Or should a package come with both, a pyproject.toml and a setup.py?
How would one install a project with pyproject.toml in an editable state?

Answer 1

Yes, pyproject.toml is the specified file format of PEP 518 which contains the build system requirements of Python projects.

This solves the build-tool dependency chicken and egg problem, i.e. pip can read pyproject.toml and what version of setuptools or wheel one may need.

If you need a setup.py for an editable install, you could use a shim in setup.py:

#!/usr/bin/env python

import setuptools

if __name__ == "__main__":
    setuptools.setup()