Resources for annotating third party Django libraries

[coiax]

In our project, we're using django-enumfield, and their custom field.

Currently, the custom field is typed as an Any. The get type should be the specific Enum that you associate with the field, while the set type should be Union[int, MyEnum].

Some resources on how to write stubs for third party libraries would be really helpful!

[sobolevn]

You can try to use class-level attribute annotation with Field: https://github.com/typeddjango/django-stubs/blob/master/django-stubs/db/models/fields/__init__.pyi#L45

It is a generic type with two parameters:

• _ST for types that can be used when settings a value
• _GT as a type that will be returned when getting a value

Something like:

my_attr: Field[SupportsInt, str] = MyCustomIntField()

Can you please report if this works for you? If so, I will add this example to FAQ.

[coiax]

I tried to make a test setup, with the snippet you suggested, my results are in this gist.

https://gist.github.com/coiax/e4a26eb224c97b33cfb303f1df2f9fe0

Typing the field with Field[Union[int, Colour], Colour] only provides typing coverage when using an instance of the object, but looks like there's trouble with other ways of engaging with the object, unless I set up my test environment wrong!

[sobolevn]

Thanks! Can you please also attach mypy output to your gist?

[coiax]

Done.

[flaeppe]

With all of its quirks and limitations. Just as a reference, this is how I annotated a package with a model field: https://github.com/flaeppe/django-choicefield/