How to use Python type hints with Django QuerySet?

Question

Is it possible to specify type of records in Django QuerySet with Python type hints? Something like QuerySet[SomeModel]?

For example, we have model:

Answer 1

There's a special package called django-stubs (the name follows PEP561) to type your django code.

That's how it works:

# server/apps/main/views.py
from django.http import HttpRequest, HttpResponse
from django.shortcuts import render

def index(request: HttpRequest) -> HttpResponse:
    reveal_type(request.is_ajax)
    reveal_type(request.user)
    return render(request, 'main/index.html')

Output:

» PYTHONPATH="$PYTHONPATH:$PWD" mypy server
server/apps/main/views.py:14: note: Revealed type is 'def () -> builtins.bool'
server/apps/main/views.py:15: note: Revealed type is 'django.contrib.auth.models.User'

And with models and QuerySets:

# server/apps/main/logic/repo.py
from django.db.models.query import QuerySet

from server.apps.main.models import BlogPost

def published_posts() -> 'QuerySet[BlogPost]':  # works fine!
    return BlogPost.objects.filter(
        is_published=True,
    )

Output:

reveal_type(published_posts().first())
# => Union[server.apps.main.models.BlogPost*, None]

• Complete tutorial: https://sobolevn.me/2019/08/typechecking-django-and-drf
• Types for django: https://github.com/typeddjango/django-stubs
• Types for drf: https://github.com/typeddjango/djangorestframework-stubs