The `num_args` argument was introduced in b6812f2d9d1bea3bdc9c5f9a747c5c71c764fa0f specifically for `get_callable` (note how it can take two arguments but the `num_args` is 1).

I suspect there might be something weird going on but I haven't had time to look into it and unfortunately, we cannot ask the original committer of that change anymore :(