Model.object and djangos @classproperties not working since 1.13.1

[djbrown]

Bug report

Hello :-) first of all thank you very much for releasing the new version 1.13.1 so quickly after I asked for it!
But now I am facing two new problems, which might be related so I'm posting them together.

Steps to reproduce

See my separately crafted repo with minimal steps to reproduce:
https://github.com/djbrown/mypy-django-bugs

But basically it's:

• pip install django mypy django-stubs==1.13.0
• generate simple django project and include above bug snippets
• execute mypy check -> ✔
• pip install django-stubs==1.13.1
• execute mypy check -> ❌
• pip install django-stubs==1.13.0
• execute mypy check -> ✔

So it's definitely the new version..
I can also add a failing test or workflow so you don't have to reproduce manually.

[Collapsed: This part of the report was resolved]

no attribute Model.objects

from django.db.models import Model
def invalid(model: Model):
    model.objects

Results in error: "Model" has no attribute "objects" [attr-defined]
I already tried to fix by enabling monkey-patching in settings.py or module via django_stubs_ext or use ModelBase or TypeVar instead of Model.
Because in #1150 the object property was moved from Model to ModelBase - but that doesn't work for me.

Maybe also related issues:

• "Type[Model]" has no attribute "objects" (again?) #83
• What's the best way to write a type hint for any kind of model object? #1068
  • "Type[Model]" has no attribute "objects" #16

cannot access classproperties

from django.test import LiveServerTestCase
class ServerTestCase(LiveServerTestCase):
    def invalid(self, arg: str):
        self.live_server_url

Results in:

error: Argument 1 to "__get__" of "classproperty" has incompatible type "ServerTestCase"; expected "Optional[classproperty[Any]]"  [arg-type]
error: Argument 2 to "__get__" of "classproperty" has incompatible type "Type[ServerTestCase]"; expected "Type[classproperty[Any]]"  [arg-type]

I already tried to fix by enabling monkey-patching in settings.py or module via django_stubs_ext, or access classproperty via class or super class.
Accessing normal class attributes works fine though.

System information

• OS: ubuntu
• python version: 3.10.4
• django version: 4.1.4
• mypy version: 0.991
• django-stubs version: 1.13.1
• django-stubs-ext version: 0.7.0

[djbrown]

A possible workaround would be to to remove the type hints. That probably signals mypy to leave out the function.
I decided to comment-ignore the problematic lines until this is resolved.

[intgr]

from django.db.models import Model
def invalid(model: Model):
    model.objects

Results in error: "Model" has no attribute "objects" [attr-defined]

This error is correct. model: Model tells mypy that the variable is an instance of Model.

Only Model classes have this attribute, not instances.

Try def invalid(model: Type[Model]):

[intgr]

As for the classproperty case, I am not sure what is happening there.

[djbrown]

ahhh thank you, that's correct! the Model.object problem is fixed now :-)

[intgr]

@dlesbre Please open a separate issue, tracking multiple different problems in one issue gets messy.

[dlesbre]

@dlesbre Please open a separate issue, tracking multiple different problems in one issue gets messy.

Done #1286

[djbrown]

The stub for django.test.testcases.LiveServerTestCase looks currenty look like this:

django-stubs/django-stubs/test/testcases.pyi

Lines 256 to 265 in 090aea6

	class LiveServerTestCase(TransactionTestCase):
	host: str
	port: int
	server_thread_class: type[Any]
	server_thread: Any
	static_handler: Any
	@classproperty
	def live_server_url(cls: Any) -> str: ...
	@classproperty
	def allowed_host(cls: Any) -> str: ...

mypy complains about the accessed classproperties e.g. live_server_url or allowed_host,
but the normal class attributes can be used just fine e.g. port, host ...

I tried to set some other type hints instead of cls: Any (e.g. type, type[Any] or type[Self]) or use TypeVar or remove the annotation in the local testcases.pyi stub file, but only got slightly different mypy error: ... expected "Optional[classproperty[<nothing>]]"

What kind of did work, was to replace @classproperty with @classmethod but then I had to add parenthesis to my actual source code (live_server_url()) and that doesn't match the django implementation.
The code wont actually work that way, so this is not a solution, but maybe someone can find a proper solution with that.
Maybe djangos custom @classproperty decorator has to be typed differently? It's not from the standard python library..

The python typing docs say:

Do not annotate self and cls in method definitions, except when referencing a type variable.

So I guess the cls: type[Self] annotation in other classmethods should be removed too, since they don't use type variables.

[djbrown]

What finally did work for me (based on my previous comments last concerns) was to just set the classproperties as simple attributes in the type stub without any decorators:

class LiveServerTestCase(TransactionTestCase): 
    host: str 
    port: int 
    ...
    live_server_url: str
    allowed_host: str

I will create a pull request for that and hope you agree to this solution.
Alternatively someone will have to think about how to properly annotate djangos classproperties..

[intgr]

The LiveServerTestCase and classproperty classes don't seem to have changed between 0.13.0...1.13.1. Are you sure this regressed in 1.13.1?

Edit: Oh, sorry, I had some old commit checked out. I think I see the bug now.

[intgr]

Indeed, classproperty was broken, fixed in #1287.

[djbrown]

thanks :) I reviewed your PR and applied the patch locally. that fixes the problem too - and more correctly :)