t option and custom option arguments are tricky to handle correctly about ocaml_python_bindgen

[mooreryan]

The other thing to keep in mind is if you have a Python function that returns either a custom object or None, the t option return type will be wrong too.

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def maybe_make_friend(self, color):
        if color == 'orange':
            return(Person(f'{self.name}\'s friend, Orange Soda', 33))
        else:
            return(None)

You would think to bind it like this:

  val maybe_make_friend : t -> color:string -> unit -> t option

That generates

  let maybe_make_friend t ~color () =
    let callable = Py.Object.find_attr_string t "maybe_make_friend" in
    let kwargs = filter_opt [ Some ("color", Py.String.of_string color) ] in
    of_pyobject @@ Py.Callable.to_function_with_keywords callable [||] kwargs

When the user is expecting it to generate something more like this:

let f t () =
  let callable = Py.Object.find_attr_string t "f" in
  let kwargs = filter_opt [ ] in
  (fun x -> if Py.is_none x then None else Some (of_pyobject x))
  @@ Py.Callable.to_function_with_keywords callable [||] kwargs

As above it has to do with the way --of-pyo-ret-type is working with things. And the fact that t and custom types are treating differently from something like int option.