[aleksanb]

It's quite useful on ci, and as a `make mypy` can run before pushing up your code, but for interactive errors we all use pyright, which is a bit of a letdown because you don't get autocomplete for fields and models accessed through reverse relation managers etc, pyright doesn't know about them. Many packages ship types nowadays, so the type coverage isn't too bad for us right now.

Here's our plugin setup in mypy.ini in case this helps (Django 4.2 + drf 3.14)

  [mypy]
  plugins =
      mypy_django_plugin.main,
      mypy_drf_plugin.main
  ignore_missing_imports = True
  follow_imports = silent
  no_implicit_optional = True
  warn_unused_ignores = True
  check_untyped_defs = True
  disallow_untyped_defs = True
  disallow_untyped_calls = True
  warn_unreachable = True
  strict_equality = True
  allow_redefinition = True
  show_error_codes = True
  mypy_path = stubs
  
  [mypy.plugins.django-stubs]
  django_settings_module = 'mycompany.settings'

with packages:

  mypy==1.6.0
  django-stubs==4.2.4
  django-stubs-ext==4.2.2
  djangorestframework-stubs==3.14.3

with this horror of a regex in make (because you'll get drowned in wrong type errors in all of the untype files, and errors get shown from imports even if you don't care about that imported file), add more file targets as necessary:

  FILES_TO_MYPY = $(shell ls mycompany/\*/validators.py mycompany/\*/services.py mycompany/\*/selectors.py mycompany/\*/managers.py | sort | uniq)

  # 1)We have to grep out django-manager-missing like this until the following bug
  # is fixed: https://github.com/python/mypy/issues/12987.
  # 2) We grep out the line of `Found 95 errors in 16 files (checked 83 source
  # files)` that now appears as we use follow-imports: silent, because there's a
  # bug where errors from imported modules are counted against the total even
  # though they aren't emitted. If any real errors appear we get them as a
  # separate line anyways.
  .PHONY: mypy
  mypy:
   @{ MYPY_FORCE_COLOR=${NOT_CI} $(VENV)/bin/mypy --config-file mypy.ini $(FILES_TO_MYPY) 2>&3 | grep -v 'django-manager-missing\|errors in'; } 3>&1 | tee $(HYRE_TESTS_OUTPUT_PATH)/mypy.stdout.txt

This allows you to get proper errors for things like

  model = MyModel.objects.get()
  othermodel = model.othermodel_set.first()
  reveal_type(othermodel)  # correctly revealed to note: Revealed type is "Union[mycompany.importpath.models.OtherModel None]"

and even errors on typos like

  model = MyModel.objects.get()
  othermodel = model.ooooothermodel_set.first()  # revealed as MyModel has no attribute ooooothermodel_set, perhaps you ment othermodel_set
.