[Python-Dev] [Python-checkins] cpython: Issue #14127: Add ns= parameter to utime, futimes, and lutimes.

[Stefan Krah]

Larry Hastings <larry at hastings.org> wrote:
> On 05/03/2012 10:07 PM, Benjamin Peterson wrote:
> 
>         +    if (times && ns) {
>         +        PyErr_Format(PyExc_RuntimeError,
> 
>     Why not a ValueError or TypeError?
> 
> 
> Well it's certainly not a TypeError.  The 3.2 documentation defines TypeError
> as:
> 
>     Raised when an operation or function is applied to an object of
>     inappropriate type. The associated value is a string giving details about
>     the type mismatch.
> 
> If someone called os.utime with both times and ns, and the values of each would
> have been legal if they'd been passed in in isolation, what would be the type
> mismatch?

I had the same question a while ago, and IIRC Raymond said that the convention
is to raise a TypeError if a combination of arguments cannot be handled by a
function.

In OCaml this would be quite natural:

$ ocaml
        Objective Caml version 3.12.0
# type kwargs = TIMES | NS;;
type kwargs = TIMES | NS

let utime args =
  match args with
  | (_, TIMES) -> "Got times"
  | (_, NS) -> "Got NS";;
      val utime : 'a * kwargs -> string = <fun>

# utime ("/etc/passwd", TIMES);;
- : string = "Got times"
# utime ("/etc/passwd", NS);;
- : string = "Got NS"
# utime ("/etc/passwd", TIMES, NS);;
Error: This expression has type string * kwargs * kwargs
       but an expression was expected of type 'a * kwargs


In Python it makes sense if (for the purpose of raising an error) one assumes
that {"times":(0, 0)}, {"ns":(0, 0)} and {"times":(0, 0), "ns":(0, 0)} have
different types.



Stefan Krah