It doesn't. There are cases where the type-checker can't know the type (e.g. json.load has to return Any), but there are tools in the language to reduce how much that happens. If you commit to a fully strictly-typed codebase, it doesn't happen often.

You can actually annotate the return type of json.load better than that:

    JSON = float | bool | int | str | None | list[“JSON”] | dict[str, “JSON”]