Add pyproject toml

[maxnoe]

Reference for pyproject.toml and why we should have one:
https://www.python.org/dev/peps/pep-0518/
https://www.python.org/dev/peps/pep-0517/
https://snarky.ca/what-the-heck-is-pyproject-toml/

[codecov]

Codecov Report

Merging #1246 into master will not change coverage by %.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1246   +/-   ##
=======================================
  Coverage   86.69%   86.69%           
=======================================
  Files         192      192           
  Lines       11900    11900           
=======================================
  Hits        10317    10317           
  Misses       1583     1583           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e7bb1a4...f64eab9. Read the comment docs.

[kosack]

Should we put any other config in there while we're at it? Like black configs? (https://github.com/psf/black/blob/master/pyproject.toml) - the defaults are pretty much correct, but it might be nice to specify only the python version we support so it uses modern features when possible, and also to exclude files it shoudn't format when running in recursive mode. Soon I would like to install it as a pre-commit hook, after we reformat all code, so we fix all small style problems. If the config is already there, that would help.

[kosack]

I guess this can eventually replace setup.py, but it seems like the features are not all there yet (installing in developer mode for example). I wonder if conda will support it eventually? Right now, I build the conda package in a pretty automated fashion, reading the necessary info from setup.py, but that will break I guess if we go full PEP 517

[maxnoe]

There is no "full" pep 517. You need a build system. You can now specify that build system in the pyproject.toml.

But you still have to choose setuptools, or poetry or something else.
We could think about switching to poetry. But I think that's another matter.
For setuptools based builds, you still need setup.py

[maxnoe]

I added the black config

[kosack]

There is no "full" pep 517. You need a build system. You can now specify that build system in the pyproject.toml.

What I meant was this quote here from the article above:

But there's a bonus if you use a pyproject.toml file with a setup.cfg configuration for setuptools: you don't need a setup.py file anymore!

Right now we have a mix of setup.py, setup.cfg, and pyproject.toml. But I guess that's fine for now.

[maxnoe]

Ah ok. But we probably want to keep the automatic versioning, right? So that needs a script, not just a config.

[watsonjj]

Does this address #1159?

[maxnoe]

@watsonjj right now, it just adds a config, it does not run black by itself