pythongh-122272: guarantee specifiers %F and %C for datetime.strftime to be 0-padded

Author: blhsing

Lib/_pydatetime.py

@@ -272,14 +272,19 @@ def _wrap_strftime(object, format, timetuple):
                                 # strftime is going to have at this: escape %
                                 Zreplace = s.replace('%', '%%')
                     newformat.append(Zreplace)
-                elif ch in 'YG' and object.year < 1000 and _need_normalize_century():
-                    # Note that datetime(1000, 1, 1).strftime('%G') == '1000' so
-                    # year 1000 for %G can go on the fast path.
+                # Note that datetime(1000, 1, 1).strftime('%G') == '1000' so
+                # year 1000 for %G can go on the fast path.
+                elif ch in 'YGFC' and object.year < 1000 and _need_normalize_century():
                     if ch == 'G':
                         year = int(_time.strftime("%G", timetuple))
                     else:
                         year = object.year
-                    push('{:04}'.format(year))
+                    if ch == 'C':
+                        push('{:02}'.format(year // 100))
+                    else:
+                        push('{:04}'.format(year))
+                        if ch == 'F':
+                            push('-{:02}-{:02}'.format(*timetuple[1:3]))
                 else:
                     push('%')
                     push(ch)

Lib/test/datetimetester.py

@@ -1710,13 +1710,19 @@ def test_strftime_y2k(self):
             (1000, 0),
             (1970, 0),
         )
-        for year, offset in dataset:
-            for specifier in 'YG':
+        for year, g_offset in dataset:
+            for specifier in 'YGFC':
                 with self.subTest(year=year, specifier=specifier):
                     d = self.theclass(year, 1, 1)
                     if specifier == 'G':
-                        year += offset
-                    self.assertEqual(d.strftime(f"%{specifier}"), f"{year:04d}")
+                        year += g_offset
+                    if specifier == 'C':
+                        expected = f"{year // 100:02d}"
+                    else:
+                        expected = f"{year:04d}"
+                        if specifier == 'F':
+                            expected += f"-01-01"
+                    self.assertEqual(d.strftime(f"%{specifier}"), expected)
 
     def test_replace(self):
         cls = self.theclass

Modules/_datetimemodule.c

@@ -1852,8 +1852,10 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
     Py_ssize_t ntoappend;       /* # of bytes to append to output buffer */
 
 #ifdef Py_NORMALIZE_CENTURY
-    /* Buffer of maximum size of formatted year permitted by long. */
-    char buf[SIZEOF_LONG*5/2+2];
+    /* Buffer of maximum size of formatted year permitted by long.
+     * Adding 6 just to accomodate %F with dashes, 2-digit month and day.
+     */
+    char buf[SIZEOF_LONG*5/2+2+6];
 #endif
 
     assert(object && format && timetuple);
@@ -1950,7 +1952,7 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
             ntoappend = PyBytes_GET_SIZE(freplacement);
         }
 #ifdef Py_NORMALIZE_CENTURY
-        else if (ch == 'Y' || ch == 'G') {
+        else if (ch == 'Y' || ch == 'G' || ch == 'F' || ch == 'C') {
             /* 0-pad year with century as necessary */
             PyObject *item = PyTuple_GET_ITEM(timetuple, 0);
             long year_long = PyLong_AsLong(item);
@@ -1980,8 +1982,26 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
                     goto Done;
                 }
             }
-
-            ntoappend = PyOS_snprintf(buf, sizeof(buf), "%04ld", year_long);
+            if (ch == 'F') {
+                item = PyTuple_GET_ITEM(timetuple, 1);
+                long month = PyLong_AsLong(item);
+                if (month == -1 && PyErr_Occurred()) {
+                    goto Done;
+                }                
+                item = PyTuple_GET_ITEM(timetuple, 2);
+                long day = PyLong_AsLong(item);
+                if (day == -1 && PyErr_Occurred()) {
+                    goto Done;
+                }
+                ntoappend = PyOS_snprintf(buf, sizeof(buf), "%04ld-%02ld-%02ld",
+                                          year_long, month, day);
+            }
+            else {
+                ntoappend = PyOS_snprintf(buf, sizeof(buf), "%04ld", year_long);
+                if (ch == 'C') {
+                    ntoappend -= 2;
+                }
+            }
             ptoappend = buf;
         }
 #endif