CI add pre-commit, check notebook imports are sorted

[MarcoGorelli]

closes #4077

This allows the check to be carried out without requiring users to add pre-commit, nbqa, or isort to the dev requirements.

Also, it means that once #4083 is merged, you can easily add

-   repo: https://github.com/asottile/pyupgrade
    rev: v2.7.2
    hooks:
    -   id: pyupgrade

to .pre-commit-config.yaml , and similarly for any other code-quality tool (e.g. black, flake8, you name it...) you decide to add to this amazing repo

[codecov]

Codecov Report

Merging #4088 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4088   +/-   ##
=======================================
  Coverage   88.48%   88.48%           
=======================================
  Files          88       88           
  Lines       13865    13865           
=======================================
  Hits        12268    12268           
  Misses       1597     1597           

[AlexAndorra]

Looks super nice and should make our lives easier, thanks a lot @MarcoGorelli 🎉
Approving but will merge a bit later, in case somebody else wants to comment.

Just had a couple questions:

• the pre-commit.yml file looks a bit esoteric to me -- does it come from a standard configuration or something like that?
• Does the line rev: 0.1.29 in .pre-commit-config.yaml mean that the commit hook will stay with this version of nbqa instead of just using the latest?
• Also, can you update the NB style guide accordingly once this PR is merged?

[MarcoGorelli]

Thanks Alex!

* the `pre-commit.yml` file looks a bit esoteric to me -- does it come from a standard configuration or something like that?

Yes, it's for pre-commit. If you install it, then any time you make a commit, pre-commit checks will run against the files you modified. If you don't install it, then the checks will just run during CI and won't interfere with the rest of your development. We use it in pandas https://github.com/pandas-dev/pandas/blob/master/.pre-commit-config.yaml , I find it to be a really great tool.

* Does the line `rev: 0.1.29` in `.pre-commit-config.yaml` mean that the commit hook will stay with this version of nbqa instead of just using the latest?

If you run pre-commit autoupdate from the command line, it'll update each hook to its latest version.

* Also, can you update [the NB style guide](https://github.com/pymc-devs/pymc3/wiki/PyMC's-Jupyter-Notebook-Style) accordingly once this PR is merged?

Would love to but I don't think I have permission to do so

[MarcoGorelli]

Thanks Alex!

* the `pre-commit.yml` file looks a bit esoteric to me -- does it come from a standard configuration or something like that?

Yes, it's for pre-commit. If you install it, then any time you make a commit, pre-commit checks will run against the files you modified. If you don't install it, then the checks will just run during CI and won't interfere with the rest of your development. We use it in pandas https://github.com/pandas-dev/pandas/blob/master/.pre-commit-config.yaml , I find it to be a really great tool.

Sorry, my bad, you were asking about pre-commit.yml here, not about .pre-commit-config.yaml. It comes from here https://github.com/pre-commit/action , although it seems they've now released a version 2 of this action (whose config file looks significantly less esoteric 🤣 ) so I've updated to use that one instead

[AlexAndorra]

Ha ha, indeed, this looks much better 😆 Thanks for updating!
Going to merge now, as we gave it 24h. Did you try updating the style guide though? I was under the impression that everyone could update it, but maybe I'm mistaken

[MarcoGorelli]

@AlexAndorra you're right, I was able to update it, and so have done so - thanks!

[AlexAndorra]

Thanks @MarcoGorelli , looks good! Do you mind also adding a line about the new pre-commit GitHub Action you set up?

[MarcoGorelli]

Sure, done @AlexAndorra - I also indented the paragraphs so markdown formats them in a more readable manner

[AlexAndorra]

Awesome, thanks again @MarcoGorelli ! Now that I think about it, it seems like we can also Black-format the NBs with nbqa, can't we? If so, we may as well add a GitHub action for that too -- would get rid of the 4th step in the style guide