Add json types to _typeshed?

[srittau]

As this is an issue that pops up quite often and would be useful in a few places in typeshed as well: Should we add json types to _typeshed? As recursive types aren't possible at the moment, I'd suggest something simple like this:

JsonObject = dict[str, Any]  # Any is Json
JsonArray = list[Any]  # Any is Json
Json = JsonObject | JsonArray | str | float | int | bool | None

This can be improved if recursive types become available and could be a useful placeholder if/when the stdlib gains a proper JSON type.

[srittau]

Cf. python/typing#182.

[JukkaL]

I wonder if we should have a third-party module on PyPI with only useful type definitions / aliases that can be more cleanly used in user code than importing from _typeshed. Unlike typing_extensions, these wouldn't introduce any new type system features -- it would all be just for convenience. And unlike typing_extensions, we could add arbitrary things not in typing.

[srittau]

No one is forced to use, but we can use it in our stubs. And it's an improvement over the status quo of just returning Any. Even just using Json = Any is an improvement, in my opinion.

[srittau]

@JukkaL That's actually a good idea. Just have a types-typeshed (or similar) module that can then be depended on by type checkers, third-party stubs and other packages.

[wbolster]

just for reference/inspiration, there's a mindblowing and mypy-specific hack for ‘correct’ json type checking:

python/typing#182 (comment)

[CobaltCause]

Fwiw, the following appears to work as expected with Pyright currently:

JsonScalar = None | int | float | bool | str
JsonObject = dict[str, "JsonScalar | JsonList | JsonObject"]
JsonList = list["JsonScalar | JsonObject | JsonList"]
Json = JsonScalar | JsonList | JsonObject

I think this version allows all the possible cases and nothing else based on the conversion table here.

[hauntsaninja]

See also python/typing#182 (comment)

I think we can close this, since we shouldn't add anything to typeshed. I'd accept a PR adding JSON and JSON_ro from that message to https://github.com/hauntsaninja/useful_types/