[Python-Dev] Using argument clinic to replace timemodule.c:parse_time_t_args()

[Nikolaus Rath]

Larry Hastings <larry at hastings.org> writes:
> On 01/18/2014 09:52 PM, Ryan Smith-Roberts wrote:
>>
>> I still advise you not to use this solution. time() is a system call
>> on many operating systems, and so it can be a heavier operation than
>> you'd think. Best to avoid it unless it's needed (on FreeBSD it
>> seems to add about 15% overhead to localtime(), for instance).
>>
>
> I agree.  Converting to Argument Clinic should not cause a performance
> regression.  Please don't add new calls to time() for the sake of
> making code more generic.
>
> A better choice would be to write a converter function in C, then use
> a custom converter that called it.  Nikolaus: Is that something you're
> comfortable doing?

I think I'll need some help. I don't know how to handle the case where
the user is not passing anything.

Here's my attempt:

,----
| /* C Converter for argument clinic
|    If obj is NULL or Py_None, return current time. Otherwise,
|    convert Python object to time_t.
| */
| static int
| PyObject_to_time_t(PyObject *obj, time_t *stamp)
| {
|     if (obj == NULL || obj == Py_None) {
|         *stamp = time(NULL);
|     }
|     else {
|         if (_PyTime_ObjectToTime_t(obj, stamp) == -1)
|             return 0;
|     }
|     return 1;
| } 
| 
| /*[python input]
| class time_t_converter(CConverter):
|     type = 'time_t'
|     converter = 'PyObject_to_time_t'
|     default = None
| [python start generated code]*/
| /*[python end generated code: checksum=da39a3ee5e6b4b0d3255bfef95601890afd80709]*/
| 
|     
| /*[clinic input]
| time.gmtime
| 
|     seconds: time_t
|     /
| 
| [clinic start generated code]*/
`----

but this results in the following code:

,----
| static PyObject *
| time_gmtime(PyModuleDef *module, PyObject *args)
| {
|     PyObject *return_value = NULL;
|     time_t seconds;
| 
|     if (!PyArg_ParseTuple(args,
|         "|O&:gmtime",
|         PyObject_to_time_t, &seconds))
|         goto exit;
|     return_value = time_gmtime_impl(module, seconds);
| 
| exit:
|     return return_value;
| }
`----

This works if the user calls time.gmtime(None), but it fails for
time.gmtime(). It seems that in that case my C converter function is
never called.

What's the trick that I'm missing?


Thanks!
-Nikolaus

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