mypy-django-example

A demo project for django-mypy

This repository contains an implementation of the django 1.10 tutorial extended with PEP-484 type annotations. It's goal is to be used as an example and demonstration of the mypy-django type stubs project. See the README file at https://github.com/machinalis/mypy-django for more details

Usage

To typecheck this you should install mypy-django and run:

$ mypy --strict-optional -p polls
polls/apps.py:1: error: No library stub file for module 'django.apps'
polls/apps.py:1: note: (Stub files are from https://github.com/python/typeshed)
polls/models.py:3: error: No library stub file for module 'django.db'
polls/tests.py:4: error: No library stub file for module 'django.test'
polls/views.py:1: error: No library stub file for module 'django.db.models.query'
polls/views.py:4: error: No library stub file for module 'django.shortcuts'
$ mypy --strict-optional -p tutorial
tutorial/urls.py:17: error: No library stub file for module 'django.contrib'
tutorial/urls.py:17: note: (Stub files are from https://github.com/python/typeshed)
tutorial/wsgi.py:12: error: No library stub file for module 'django.core.wsgi'

The error messages known shown above are expected (They just mention that mypy-django doesn't cover some of the django modules).

If you need information about how to run this as a project you should probably follow the django tutorial itself.

Using type annotations

If you take a look at the repo and its commits, you'll see how annotations were added and can be useful as an example of what to expect when annotating your own code.

Most of the changes consist mainly in adding types to view, namely a request: HttpRequest argument and a return value -> HttpResponse. See for example 60c1ff4.

Other functions/methods that are now views can usually be annotated in a fairly simple and obvious way, see for example 74335dd, 07a8f6b or b18aa7b

What follows is a list of trickier cases

• You need to provide a type for settings.ALLOWED HOSTS if left empty, see e6fdfab
• You need to modify migrations with no dependencies and also add a # type: List[Tuple[str, str]] annotation to tis dependencies field, see 6b8f15a
• You may want to # type: ignore some of the imported modules that have no type stubs to avoid warning messages. See fb2e1f4
• Some complicated/deep structures containing None values can produce some warnings that can be avoided by giving more detailed annotations. See for example this case with ModelAdmin.fieldsets: abb3ab0
• Setting attributes to function objects (something you do if you use them in admin modules, for example for a list_display) is not very well supported by mypy. You can see that I workarounded that at abb3ab0. There is an open issue at the mypy tracker about this.