pep484 stubs for Django

This package contains type stubs and a custom mypy plugin to provide more precise static types and type inference for Django framework. Django uses some Python "magic" that makes having precise types for some code patterns problematic. This is why we need this project. The final goal is to be able to get precise types for most common patterns.

Installation

pip install django-stubs[compatible-mypy]

To make mypy aware of the plugin, you need to add

[mypy]
plugins =
    mypy_django_plugin.main

[mypy.plugins.django-stubs]
django_settings_module = "myproject.settings"

in your mypy.ini or setup.cfg file.

pyproject.toml configurations are also supported:

[tool.mypy]
plugins = ["mypy_django_plugin.main"]

[tool.django-stubs]
django_settings_module = "myproject.settings"

Two things happening here:

We need to explicitly list our plugin to be loaded by mypy
Our plugin also requires django settings module (what you put into DJANGO_SETTINGS_MODULE variable) to be specified

This fully working typed boilerplate can serve you as an example.

Version compatibility

We rely on different django and mypy versions:

django-stubs	Mypy version	Django version	Django partial support	Python version
4.2.0	1.2.x	4.2	4.1, 4.0, 3.2	3.7 - 3.11
1.16.0	1.1.x	4.1	4.0, 3.2	3.7 - 3.11
1.15.0	1.0.x	4.1	4.0, 3.2	3.7 - 3.11
1.14.0	0.990+	4.1	4.0, 3.2	3.7 - 3.11

Features

Type checking of Model Meta attributes

By inheriting from the TypedModelMeta class, you can ensure you're using correct types for attributes:

from django.db import models
from django_stubs_ext.db.models import TypedModelMeta

class MyModel(models.Model):
    example = models.CharField(max_length=100)

    class Meta(TypedModelMeta):
        ordering = ["example"]
        constraints = [
            models.UniqueConstraint(fields=["example"], name="unique_example"),
        ]

FAQ

Is this an official Django project?

No, it is not. We are independent from Django at the moment. There's a proposal to merge our project into the Django itself. You can show your support by liking the PR.

Is it safe to use this in production?

Yes, it is! This project does not affect your runtime at all. It only affects mypy type checking process.

But, it does not make any sense to use this project without mypy.

mypy crashes when I run it with this plugin installed

The current implementation uses Django's runtime to extract information about models, so it might crash if your installed apps or models.py are broken.

In other words, if your manage.py runserver crashes, mypy will crash too. You can also run mypy with --tb option to get extra information about the error.

I cannot use QuerySet or Manager with type annotations

You can get a TypeError: 'type' object is not subscriptable when you will try to use QuerySet[MyModel], Manager[MyModel] or some other Django-based Generic types.

This happens because these Django classes do not support __class_getitem__ magic method in runtime.

You can go with our django_stubs_ext helper, that patches all the types we use as Generic in django.

Install it:
```
pip install django-stubs-ext  # as a production dependency
```
And then place in your top-level settings:
```
import django_stubs_ext

django_stubs_ext.monkeypatch()
```
Note: This monkey patching approach will only work when using Python 3.7 and higher, when the __class_getitem__ magic method was introduced.

You can add extra types to patch with django_stubs_ext.monkeypatch(extra_classes=[YourDesiredType])
You can use strings instead: 'QuerySet[MyModel]' and 'Manager[MyModel]', this way it will work as a type for mypy and as a regular str in runtime.

How can I create a HttpRequest that's guaranteed to have an authenticated user?

Django's built in HttpRequest has the attribute user that resolves to the type

Union[User, AnonymousUser]

where User is the user model specified by the AUTH_USER_MODEL setting.

If you want a HttpRequest that you can type-annotate with where you know that the user is authenticated you can subclass the normal HttpRequest class like so:

from django.http import HttpRequest
from my_user_app.models import MyUser


class AuthenticatedHttpRequest(HttpRequest):
    user: MyUser

And then use AuthenticatedHttpRequest instead of the standard HttpRequest for when you know that the user is authenticated. For example in views using the @login_required decorator.

My QuerySet methods are returning Any rather than my Model

If you are using MyQuerySet.as_manager():

Example:

from django.db import models

class MyModelQuerySet(models.QuerySet):
    pass


class MyModel(models.Model):
    bar = models.IntegerField()
    objects = MyModelQuerySet.as_manager()


def use_my_model() -> int:
    foo = MyModel.objects.get(id=1) # Should now be `MyModel`
    return foo.xyz # Gives an error

Or if you're using Manager.from_queryset:

Example:

from django.db import models


class MyModelQuerySet(models.QuerySet):
    pass


MyModelManager = models.Manager.from_queryset(MyModelQuerySet)


class MyModel(models.Model):
    bar = models.IntegerField()
    objects = MyModelManager()


def use_my_model() -> int:
    foo = MyModel.objects.get(id=1) # Should now be `MyModel`
    return foo.xyz # Gives an error

Why am I getting incompatible return type errors on my custom managers?

If you declare your custom managers without generics and override built-in methods you might see an error message about incompatible error messages, something like this:

from django.db import models

class MyManager(model.Manager):
    def create(self, **kwargs) -> "MyModel":
        pass

will cause this error message:

error: Return type "MyModel" of "create" incompatible with return type "_T" in supertype "BaseManager"

This is happening because the Manager class is generic, but without specifying generics the built-in manager methods are expected to return the generic type of the base manager, which is any model. To fix this issue you should declare your manager with your model as the type variable:

class MyManager(models.Manager["MyModel"]):
    ...

How do I annotate cases where I called QuerySet.annotate?

Django-stubs provides a special type, django_stubs_ext.WithAnnotations[Model], which indicates that the Model has been annotated, meaning it allows getting/setting extra attributes on the model instance.

Optionally, you can provide a TypedDict of these attributes, e.g. WithAnnotations[MyModel, MyTypedDict], to specify which annotated attributes are present.

Currently, the mypy plugin can recognize that specific names were passed to QuerySet.annotate and include them in the type, but does not record the types of these attributes.

The knowledge of the specific annotated fields is not yet used in creating more specific types for QuerySet's values, values_list, or filter methods, however knowledge that the model was annotated is used to create a broader type result type for values/values_list, and to allow filtering on any field.

from typing import TypedDict
from django_stubs_ext import WithAnnotations
from django.db import models
from django.db.models.expressions import Value


class MyModel(models.Model):
    username = models.CharField(max_length=100)


def func(m: WithAnnotations[MyModel]) -> str:
    return m.asdf  # OK, since the model is annotated as allowing any attribute


func(MyModel.objects.annotate(foo=Value("")).get(id=1))  # OK
func(
    MyModel.objects.get(id=1)
)  # Error, since this model will not allow access to any attribute


class MyTypedDict(TypedDict):
    foo: str


def func2(m: WithAnnotations[MyModel, MyTypedDict]) -> str:
    print(m.bar)  # Error, since field "bar" is not in MyModel or MyTypedDict.
    return m.foo  # OK, since we said field "foo" was allowed


func(MyModel.objects.annotate(foo=Value("")).get(id=1))  # OK
func(MyModel.objects.annotate(bar=Value("")).get(id=1))  # Error

How do I check if something is an instance of QuerySet in runtime?

A limitation of making QuerySet generic is that you can not use it for isinstance checks.

from django.db.models.query import QuerySet

def foo(obj: object) -> None:
    if isinstance(obj, QuerySet): # Error: Parameterized generics cannot be used with class or instance checks
        ...

To get around with this issue without making QuerySet non-generic, Django-stubs provides django_stubs_ext.QuerySetAny, a non-generic variant of QuerySet suitable for runtime type checking:

from django_stubs_ext import QuerySetAny

def foo(obj: object) -> None:
    if isinstance(obj, QuerySetAny):  # OK
        ...

Why am I getting incompatible argument type mentioning `_StrPromise`?

The lazy translation functions of Django (such as gettext_lazy) return a Promise instead of str. These two types cannot be used interchangeably. The return type of these functions was therefore changed to reflect that.

If you encounter this error in your own code, you can either cast the Promise to str (causing the translation to be evaluated), or use the StrPromise or StrOrPromise types from django-stubs-ext in type hints. Which solution to choose depends depends on the particular case. See working with lazy translation objects in the Django documentation for more information.

If this is reported on Django code, please report an issue or open a pull request to fix the type hints.

Related projects

awesome-python-typing - Awesome list of all typing-related things in Python.
djangorestframework-stubs - Stubs for Django REST Framework.
pytest-mypy-plugins - pytest plugin that we use for testing mypy stubs and plugins.
wemake-django-template - Create new typed Django projects in seconds.

To get help

We have Gitter here: https://gitter.im/mypy-django/Lobby If you think you have more generic typing issue, please refer to https://github.com/python/mypy and their Gitter.

Contributing

This project is open source and community driven. As such we encourage contributions big and small. You can contribute by doing any of the following:

Contribute code (e.g. improve stubs, add plugin capabilities, write tests etc) - to do so please follow the contribution guide.
Assist in code reviews and discussions in issues.
Identify bugs and issues and report these
Ask and answer questions on StackOverflow

You can always also reach out in gitter to discuss your contributions!

RyanWalker277/django-stubs