[Python-3000] PEP: rename it.next() to it.__next__(), add a next() built-in

[Brett Cannon]

On 3/6/07, Georg Brandl <g.brandl at gmx.net> wrote:
> Guido van Rossum schrieb:
> > Having now read this entire thread I am going to accept Ping's PEP.
> > Adding the sentinel argument to the next() builtin was what did it for
> > me: it neatly solves the problem if having to catch that StopIteration
> > in 99% of the cases.
>
> Attached is a possible implementation for the next() function, regardless
> of how the next method is going to be called in the future.
>
> Georg
>
>
> Index: Python/bltinmodule.c
> ===================================================================
> --- Python/bltinmodule.c        (Revision 54016)
> +++ Python/bltinmodule.c        (Arbeitskopie)
> @@ -1029,6 +1029,45 @@
>
>
>  static PyObject *
> +builtin_next(PyObject *self, PyObject *args)
> +{
> +       PyObject *it, *res;
> +       PyObject *def = NULL;
> +
> +       if (!PyArg_UnpackTuple(args, "next", 1, 2, &it, &def))
> +               return NULL;
> +       if (!PyIter_Check(it)) {
> +               PyErr_Format(PyExc_TypeError,
> +                       "%.200s object is not an iterator", it->ob_type->tp_name);
> +               return NULL;
> +       }
> +
> +       res = (*it->ob_type->tp_iternext)(it);
> +       if (res == NULL) {
> +               if (def) {
> +                       if (PyErr_Occurred() &&
> +                           !PyErr_ExceptionMatches(PyExc_StopIteration))
> +                               return NULL;
> +                       Py_INCREF(def);
> +                       return def;
> +               } else if (PyErr_Occurred()) {
> +                       return NULL;
> +               } else {
> +                       PyErr_SetNone(PyExc_StopIteration);
> +                       return NULL;
> +               }
> +       }
> +       return res;
> +}

http://docs.python.org/dev/api/type-structs.html#l2h-1017 doesn't say
that a NULL return can be used as a signal that iterator is exhausted
without raising StopIteration.  That would mean the above could be
simplified somewhat in terms of return value checking.

-Brett