Fix time calculation in the PRs script

[milancurcic]

While preparing #357 I found a small issue in the PRs script which manifests only in December. This PR fixes it and adds a requirements.txt file to keep track of the script dependencies.

We should also have a short guide on making a newsletter, which is for another PR.

[zmoon]

Oops, sorry about that, and thanks for fixing! We could do it with div-rem math and avoid dateutil, but that would be less clear.

[zmoon]

could add python-dateutil to this note? or remove the line, as maybe it won't be necessary after the documentation you mentioned is added

[milancurcic]

Yes. I've added requirements.txt which tracks dependencies, but we haven't yet documented this. So for now, I think it's good to mention it here, until it's documented elsewhere.

[zmoon]

convention would be to put this after import github, to stress that it is not part of the std lib

[awvwgk]

I recommend to just run a formatter (black or similar) over the script.

[milancurcic]

Either sounds good. I haven't used formatters before.

[zmoon]

We could add a pre-commit config to do it automatically.

e.g.

# .pre-commit-config.yaml
repos:
  - repo: https://github.com/pre-commit/pre-commit-hooks
    rev: 'v4.1.0'
    hooks:
      - id: check-yaml
      - id: trailing-whitespace
        args: ['--markdown-linebreak-ext=md,markdown']
      - id: end-of-file-fixer

  - repo: https://github.com/asottile/reorder_python_imports
    rev: 'v2.6.0'
    hooks:
      - id: reorder-python-imports

  - repo: https://github.com/psf/black
    rev: '21.12b0'
    hooks:
      - id: black

☝️ Probably as separate PR since the eof check and trailing-whitespace would probably catch other files (if checking the whole repo).

[milancurcic]

I ran it through black. Let me know if there's anything else.

[zmoon]

Maybe the requirements.txt should go inside the _scripts directory?

[milancurcic]

OK, done, let me know if it's good to go.