_StrPromise on a TypedDict

[michjnich]

Bug report

What's wrong

If I define a TypedDict

class CustomItem(TypedDict):
    name: str
    value: str

And a dict that uses this:

from django.utils.translation import gettext_lazy as _

MYDICT: dict[str, CustomItem] = {
    "test": {"name": _("testing"), "value": "this"}
}

I get the resulting message:

Incompatible types (expression has type "_StrPromise", TypedDict item "name" has type "str")

I am currently using the django_stubs_ext.StrOrPromise instead here, but the README asks us to report if we come across a _StrPromise issue while using Django.

How is that should be

I should be able to type a gettext_lazy value as str

System information

• OS: WSL2 on Win11
• python version: 3.11.6
• django version: 4.2.6
• mypy version: 1.6.1
• django-stubs version: 4.2.6
• django-stubs-ext version: 4.2.5

[flaeppe]

I should be able to type a gettext_lazy value as str

This has been brought up previously, or a slightly different version of it. Which you'll probably find if you start off somewhere around here: #689 (comment). Which is some discussion(s) and reasoning from when _StrPromise was introduced.

The short version is something like: while the promise returned by gettext_lazy in many cases behaves like a str, it doesn't always. And we want to be very careful spoofing the type checker.

[michjnich]

Ah, OK. Sorry if I've re-raised a previous discussion - I did do a search first but obviously missed those specific comments.

So for this specific case the correct solution (and will remain the correct solution) is to use StrOrPromise from django-stubs-ext? Is that right? No problem if that's the case - I'd just got the impression from the README comment that it was kind of a workaround until these things could be standardises in core.

And if you close this one, at least there's an "obvious" issue that will pop up in a search for it in the event somebody else is looking for the same thing :)

[intgr]

Yep, str and StrPromise are distinct types. If you need to typehint it in your own code, use the StrOrPromise type exported by django-stubs-ext:

from django_stubs_ext import StrOrPromise

class CustomItem(TypedDict):
    name: StrOrPromise
    value: str

[flaeppe]

No worries. As you said, now we hopefully have something that is more searchable. I'm gonna close this off for now.