Add pre-commit config

[MattiasMTS]

What has changed:

• Refactored some logic in preprocessing.py because I couldn't resist not to (I was testing the pre-commit logic on this file and just saw it, heh sorry 😋 )
• Added a .pre-commit-config.yaml which includes some nice features that are run before each commit.
  • Remove trailing whitespace (nice to have on default)
  • Consistent end-of-line fixer (might varies depending on OS and stuff).
  • check correct syntax on .yaml and .toml (indentation, etc).
  • check merge-conflict issues before continuing a rebase (nice to have if you do rebase in git)
  • Flake8 linting - checks that the changes you have done are according to the flake8 configuration. Will hopefully reduce unnecessary commits and have a clean git history.
  • mypy checker - nice to have to statically check that the hinted types in the repo is followed. Now I saw that you guys aren't using type hints that much so "if it quacks like a duck, walks like a duck, then it must be a duck!"
  • Prettier formatter on .md/.yaml files - turn e.g. single quotes ' into double quotes "'" etc.
• Split the requirement.txt file into requirement.txt and requirement-dev.txt files. Depending on if #227 gets merged, I will rebase this PR w.r.t. that one and remove these .txt and use poetry instead.

Example of pre-commit for the flake8 checker:

1. Let's say I am making some changes in the impedance.preprocessing.py file:
2. I git add and commit this feature with a nice and concise commit message, you will then see the following:

   I can see that the linting fails on flake8 with the error messages given there. Note also that the changes I made didn't get committed. I would have to resolve these before proceeding (you can skip this with --no-verify command but we keep that secret)

   

   And now it allows me to git commit this new change.

[MattiasMTS]

Just saw that the CI is failing due to splitting the requirements.txt file. This can be changed depending on #227 . For now, the reviewer can focus on the other changes.

I noticed that the tests/ folder lives in the impedance/ folder. Usually, a good practice is to have the tests folder outside the actual module folder, since it is focusing on "reflecting" the structure of the module. Furthermore, when you build and ship this package - you then install unnecessary dependency on the user. For example, this package now requires the user to install pytest since the tests folder uses it. Moving the tests folder outside and mirroring the structure of impedance allows you to easier decouple some dependencies more. Any thoughts on this @mdmurbach ?

[mdmurbach]

Just saw that the CI is failing due to splitting the requirements.txt file. This can be changed depending on #227 . For now, the reviewer can focus on the other changes.

I noticed that the tests/ folder lives in the impedance/ folder. Usually, a good practice is to have the tests folder outside the actual module folder, since it is focusing on "reflecting" the structure of the module. Furthermore, when you build and ship this package - you then install unnecessary dependency on the user. For example, this package now requires the user to install pytest since the tests folder uses it. Moving the tests folder outside and mirroring the structure of impedance allows you to easier decouple some dependencies more. Any thoughts on this @mdmurbach ?

Yeah, definitely agree (and know now) that putting the tests/ directory at the top level of the repo makes much more sense. Feel free to make that change in this PR or I can follow up after and make that change :)

PS thanks for all of your help recently getting the project from it's early hackweek state to a more robust maintainable package, definitely appreciate it and it's overdue 👍

[mdmurbach]

Going to hold off merging this one in since I think it makes sense to leverage poetry for the requirements