bpo-24416: Return named tuple from date.isocalendar() (GH-20113)

{date, datetime}.isocalendar() now return a private custom named tuple object
IsoCalendarDate rather than a simple tuple.

In order to leave IsocalendarDate as a private class and to improve what
backwards compatibility is offered for pickling the result of a
datetime.isocalendar() call, add a __reduce__ method to the named tuples that
reduces them to plain tuples. (This is the part of this PR most likely to cause
problems — if it causes major issues, switching to a strucseq or equivalent
would be prudent).

The pure python implementation of IsoCalendarDate uses positional-only
arguments, since it is private and only constructed by position anyway; the
equivalent change in the argument clinic on the C side would require us to move
the forward declaration of the type above the clinic import for whatever
reason, so it seems preferable to hold off on that for now.

bpo-24416: https://bugs.python.org/issue24416

Original PR by Dong-hee Na with only minor alterations by Paul Ganssle.

Co-authored-by: Dong-hee Na <donghee.na92@gmail.com>

1 files changed, 55 insertions, 1 deletions

diff --git a/Modules/clinic/_datetimemodule.c.h b/Modules/clinic/_datetimemodule.c.h
index 447036c..973a4ea 100644
--- a/Modules/clinic/_datetimemodule.c.h
+++ b/Modules/clinic/_datetimemodule.c.h
@@ -14,6 +14,60 @@ PyDoc_STRVAR(datetime_date_fromtimestamp__doc__,
 #define DATETIME_DATE_FROMTIMESTAMP_METHODDEF    \
     {"fromtimestamp", (PyCFunction)datetime_date_fromtimestamp, METH_O|METH_CLASS, datetime_date_fromtimestamp__doc__},
 
+static PyObject *
+iso_calendar_date_new_impl(PyTypeObject *type, int year, int week,
+                           int weekday);
+
+static PyObject *
+iso_calendar_date_new(PyTypeObject *type, PyObject *args, PyObject *kwargs)
+{
+    PyObject *return_value = NULL;
+    static const char * const _keywords[] = {"year", "week", "weekday", NULL};
+    static _PyArg_Parser _parser = {NULL, _keywords, "IsoCalendarDate", 0};
+    PyObject *argsbuf[3];
+    PyObject * const *fastargs;
+    Py_ssize_t nargs = PyTuple_GET_SIZE(args);
+    int year;
+    int week;
+    int weekday;
+
+    fastargs = _PyArg_UnpackKeywords(_PyTuple_CAST(args)->ob_item, nargs, kwargs, NULL, &_parser, 3, 3, 0, argsbuf);
+    if (!fastargs) {
+        goto exit;
+    }
+    if (PyFloat_Check(fastargs[0])) {
+        PyErr_SetString(PyExc_TypeError,
+                        "integer argument expected, got float" );
+        goto exit;
+    }
+    year = _PyLong_AsInt(fastargs[0]);
+    if (year == -1 && PyErr_Occurred()) {
+        goto exit;
+    }
+    if (PyFloat_Check(fastargs[1])) {
+        PyErr_SetString(PyExc_TypeError,
+                        "integer argument expected, got float" );
+        goto exit;
+    }
+    week = _PyLong_AsInt(fastargs[1]);
+    if (week == -1 && PyErr_Occurred()) {
+        goto exit;
+    }
+    if (PyFloat_Check(fastargs[2])) {
+        PyErr_SetString(PyExc_TypeError,
+                        "integer argument expected, got float" );
+        goto exit;
+    }
+    weekday = _PyLong_AsInt(fastargs[2]);
+    if (weekday == -1 && PyErr_Occurred()) {
+        goto exit;
+    }
+    return_value = iso_calendar_date_new_impl(type, year, week, weekday);
+
+exit:
+    return return_value;
+}
+
 PyDoc_STRVAR(datetime_datetime_now__doc__,
 "now($type, /, tz=None)\n"
 "--\n"
@@ -55,4 +109,4 @@ skip_optional_pos:
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=aae916ab728ca85b input=a9049054013a1b77]*/
+/*[clinic end generated code: output=5e17549f29a439a5 input=a9049054013a1b77]*/