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On 01/20/2014 06:44 PM, Nikolaus Rath wrote:
All in all, I'm still not sure how I'm supposed to proceed. I see the  
following options (and I'm fine with all of them):


1. Use the option group with a custom converter. This means a time(NULL)
 call even if the caller passed a parameter.


2. Declare the _impl parameter as PyObject* instead of time_t, and
 explicitly call a C conversion function.


3. Patch clinic.py to only evaluate the C default if the caller does not
 pass a parameter. This seemest cleanest, but I don't know if the
 design of clinic.py actually allows that.




clinic.py is not flexible enough to allow initialization code after
the call to the converter.



A comment on your approach so far: I'm very much against giving
"default" a default value in the constructor. I realize that hack
saves you having to say "= NULL" in a lot of places. But explicit
is better than implicit, and we're going to read these signatures a
lot more often than we write them, and I want Clinic signatures to
be easy to read at first glance.



Anyway, you're right, the converter function is not called if a
value is not passed in to convert it. I think this is more
complicated than you suspect, because PyArg_ParseWhatnot doesn't
tell you whether or not it processed a parameter. You have to
detect it yourself, generally through a clever choice of a default
value in C. But there are no illegal values of time_t.



All is not lost! What follows is rough pseudo-C code, hopefully you
can take it from here.

typedef struct {

int set;

time_t when;

} clinic_time_t;



#define DEFAULT_CLINIC_TIME_T {0, 0}


static int
parse_clinic_time_t_arg(PyObject *arg, clinic_time_t *ct)
{
 if (arg == NULL)
 return 1;
 if (arg == Py_None)
 return 0;
 if (_PyTime_ObjectToTime_t(arg, &ct->when) == -1) {
 set = 1;
 return 0;
 }
 return 1;
}


static int post_parse_clinic_time_t(clinic_time_t *ct) {
 if (ct->set)
 return 0;
 ct->when = time(NULL);
 return 0;
}


/*[python input]
class clinic_time_t_converter(CConverter):
 type = 'clinic_time_t'
 converter = 'parse_clinic_time_t'
 c_default = 'DEFAULT_CLINIC_TIME_T'
[python start generated code]*/
/*[python end generated code: checksum=...]*/


Now you can use clinic_time_t. Parameters declared clinic_time_t
can be required, or they can be optional; if they're optional give
them a default value of None. You'll have to call
post_parse_clinic_time_t() by hand in your impl function; I'll see
if I can extend Clinic so converters can emit code after a
successful call to the parse function but before the call to the
impl. Also, the converter probably isn't quite right, you'll have
to play with "impl_by_reference" and "parse_by_reference" and add
and remove asterisks and ampersands to make sure the code is 100%
correct. Examine the implementation of path_t in
Modules/posixmodule.c, as that does about the same thing.



And of course clinic_time_t is a poor name, perhaps you can come up
with a better one.



That should work,





/arry