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Mypy stubs for Django

Project description

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pep484 stubs for Django

Build status Checked with mypy Gitter StackOverflow

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

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:

  1. We need to explicitly list our plugin to be loaded by mypy
  2. 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 python version
1.10.0 0.931+ 3.2.x ^3.7
1.9.0 0.910 3.2.x ^3.6
1.8.0 0.812 3.1.x ^3.6
1.7.0 0.790 2.2.x || 3.x ^3.6
1.6.0 0.780 2.2.x || 3.x ^3.6
1.5.0 0.770 2.2.x || 3.x ^3.6
1.4.0 0.760 2.2.x || 3.x ^3.6
1.3.0 0.750 2.2.x || 3.x ^3.6
1.2.0 0.730 2.2.x ^3.6
1.1.0 0.720 2.2.x ^3.6
0.12.x old semantic analyzer (<0.711), dmypy support 2.1.x ^3.6

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.

  1. 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.

  1. 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

QuerySet.as_manager() is not currently supported.

If you are using MyQuerySet.as_manager(), then your Manager/QuerySet methods will all not be linked to your model.

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():
  foo = MyModel.objects.get(id=1) # This is `Any` but it should be `MyModel`
  return foo.xyz # No error, but there should be

There is a workaround: use Manager.from_queryset instead.

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():
  foo = MyModel.objects.get(id=1)
  return foo.xyz # Gives an error

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

Related projects

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:

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

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

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