Type Hinting Custom User Models in Django

When working with custom user models in Django, type hinting can indeed be challenging, especially with tools like Pylance in VSCode. Here are some approaches to handle this situation properly:

1. Use get_user_model() for Type Hints

Instead of directly importing your User model for type hints, you should use Django's get_user_model() function:

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from django.contrib.auth import get_user_model
from django.http import HttpRequest

User = get_user_model()

def my_func(user: User) -> None:
    print(user.is_special_user)

@login_required
def my_view(request: HttpRequest) -> None:
    my_func(request.user)  # May still show warnings

2. Type Casting for Request.user

You can use type casting to explicitly tell the type checker that request.user is of your custom User type:

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from django.contrib.auth import get_user_model
from django.http import HttpRequest
from typing import cast

User = get_user_model()

def my_func(user: User) -> None:
    print(user.is_special_user)

@login_required
def my_view(request: HttpRequest) -> None:
    user = cast(User, request.user)
    my_func(user)

3. Using Union Types for Request.user

Since request.user can be either your custom User or AnonymousUser, you can use Union types:

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from django.contrib.auth import get_user_model
from django.contrib.auth.models import AnonymousUser
from django.http import HttpRequest
from typing import Union

User = get_user_model()
UserType = Union[User, AnonymousUser]

def my_func(user: UserType) -> None:
    if hasattr(user, 'is_special_user'):
        print(user.is_special_user)

@login_required
def my_view(request: HttpRequest) -> None:
    my_func(request.user)

4. Type Checking with Assert

You can use runtime assertions to help the type checker:

PYTHONCopied
from django.contrib.auth import get_user_model
from django.http import HttpRequest

User = get_user_model()

def my_func(user: User) -> None:
    print(user.is_special_user)

@login_required
def my_view(request: HttpRequest) -> None:
    assert isinstance(request.user, User)
    my_func(request.user)

Best Practice Recommendation

The most Django-friendly approach is to use get_user_model() rather than directly referencing your User model. This ensures your code will work even if the AUTH_USER_MODEL setting is changed:

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# In a type hints file (e.g., types.py)
from django.contrib.auth import get_user_model
from django.contrib.auth.models import AnonymousUser
from typing import Union, TypeVar

UserModel = get_user_model()
UserType = Union[UserModel, AnonymousUser]
T = TypeVar('T', bound=UserModel)  # For more complex type hints

# In your views.py
from .types import UserModel, UserType

def my_func(user: UserModel) -> None:
    print(user.is_special_user)

@login_required
def my_view(request: HttpRequest) -> None:
    # Use type casting if you're sure it's a logged-in user
    from typing import cast
    user = cast(UserModel, request.user)
    my_func(user)

This approach follows Django's recommendation to always use get_user_model() when referencing the User model, ensuring your code remains compatible with different user model configurations.

Type Hinting Django's Custom User Model in VSCode/Pylance

You're encountering a common type hinting issue with Django's authentication system. The problem is that request.user can be either your custom User model or an AnonymousUser instance (when the user isn't logged in), but Pylance doesn't know this context.

Here are several approaches to solve this issue:

1. Use Type Casting

You can use explicit type casting with typing.cast:

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from typing import cast
from myapp.models import User  # Import your custom User model

def my_view(request: WSGIRequest) -> None:
    my_func(cast(User, request.user))

2. Use Type Checking

Since you're using @login_required, you know the user is authenticated:

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from django.contrib.auth.decorators import login_required
from myapp.models import User

@login_required
def my_view(request: WSGIRequest) -> None:
    user = request.user
    assert isinstance(user, User)  # This helps type checkers
    my_func(user)

3. Create a Union Type

Define a type that represents both possibilities:

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from typing import Union
from django.contrib.auth.models import AnonymousUser
from myapp.models import User

UserType = Union[User, AnonymousUser]

def my_func(user: User) -> None:
    print(user.is_special_user)

def my_view(request: WSGIRequest) -> None:
    user: UserType = request.user
    if isinstance(user, User):
        my_func(user)

4. Create a Type Guard Function

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from typing import TypeGuard
from django.contrib.auth.models import AnonymousUser
from myapp.models import User

def is_authenticated_user(user: object) -> TypeGuard[User]:
    return isinstance(user, User) and user.is_authenticated

@login_required
def my_view(request: WSGIRequest) -> None:
    if is_authenticated_user(request.user):
        my_func(request.user)  # Now typed as User

5. Create a Custom Stub File

For a more permanent solution, you could create a stub file (.pyi) that properly types Django's request object.

These approaches should help you maintain type safety while working with Django's authentication system in VSCode with Pylance.