ReadOnly

A special typing construct to mark an item of a TypedDict as read-only.

For example::

    class Movie(TypedDict):
        title: ReadOnly[str]
        year: int

    def mutate_movie(m: Movie) -> None:
        m["year"] = 1992  # allowed
        m["title"] = "The Matrix"  # type checker error

There is no runtime checking for this property.