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

Nikolaus Rath Nikolaus at rath.org
Wed Jan 22 06:13:22 CET 2014

Larry Hastings <larry at hastings.org> writes:

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

typedef struct { int set; timet when; } clinictimet; #define DEFAULTCLINICTIMET {0, 0} static int parseclinictimetarg(PyObject *arg, clinictimet *ct) { if (arg == NULL) return 1; if (arg == PyNone) return 0; if (PyTimeObjectToTimet(arg, &ct->when) == -1) { set = 1; return 0; } return 1; } static int postparseclinictimet(clinictimet *ct) { if (ct->set) return 0; ct->when = time(NULL); return 0; } /*[python input] class clinictimetconverter(CConverter): type = 'clinictimet' converter = 'parseclinictimet' cdefault = 'DEFAULTCLINICTIMET' [python start generated code]*/ /[python end generated code: checksum=...]/ Now you can use clinictimet. Parameters declared clinictimet can be required, or they can be optional; if they're optional give them a default value of None. You'll have to call postparseclinictimet() 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.

Okay, I attached a patch along these lines to the bugtracker.

However, I have to say that I lost track of what we're actually gaining with all this. If all we need is a type that can distinguish between a valid time_t value and a default value, why don't we simply use PyObject?

In other words, what's the advantage of all the code above over:

static int PyObject_to_time_t(PyObject *obj, time_t *when) { if (obj == NULL || obj == Py_None) *when = time(NULL); else if (_PyTime_ObjectToTime_t(obj, when) == -1) return 0; return 1; }

/*[clinic input] time.gmtime

seconds: object=NULL
/

[...]

static PyObject * time_gmtime_impl(PyModuleDef *module, PyObject *seconds) { PyObject *return_value = NULL; time_t when; if(!PyObj_to_time_t(seconds, &when)) return NULL;

[...]

To me this version looks shorter and clearer. Is there really an advantage in defining the clinic argument as a custom struct rather than object?

Best, -Nikolaus

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