Re: can you improve this text-only beginner copy program?

On 2025-08-28 21:15:11 +0100, Mark Bourne wrote:
> I don't know if Sphinx can extract types from type hints but, at least if
> the docstring is just for humans reading the code, using those can reduce
> the markup in the docstring:
> ```
> def copy(s: int, d: int) -> None:
>     """
>     Copy the contents of the text file whose path is given by the
>     parameter ``s`` to the text file whose path is given by ``d``.

I'm almost sure that you didn't intend the paths to be of type int.

> 
>     :param s: Path to the source text file to copy from.
>     :param d: Path to the destination text file to copy to.
>     :raises OSError: If an I/O error occurs during writing. On error,
>                      the destination file will be removed if it was
>                      partially written.
> """
> ```
> 
> Aside from acting as documentation of the expected argument and return
> types, type hints can also be read by type checkers to help find places
> where objects of the wrong types might be passed.  Type hints don't make any
> difference at runtime, so you could still call `copy(1, 2)` and it'll copy a
> file named "1" to a file named "2",

No, it would try to copy from file descriptor 1 to file descriptor 2.
Given that file descriptor 1 is normally stdout and file descriptor 2 is
stderr, this doesn't make much sense but it would work (fsvo) in a Linux
terminal.


> but type checkers would flag that as a
> possible bug - it should be `copy("1", "2")` if that's really what you
> intend.

Actually, the way you wrote it, the checker would flag the correct usage
as incorrect (and the incorrect one, too, since os.remove doesn't accept
an int).

        hjp

-- 
   _  | Peter J. Holzer    | Story must make more sense than reality.
|_|_) |                    |
| |   | [email protected]         |    -- Charles Stross, "Creative writing
__/   | http://www.hjp.at/ |       challenge!"

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