From 61c2c611ec7071c1ae19a8847877d0c0308b3fd2 Mon Sep 17 00:00:00 2001
From: Ben Hsing <blhsing@gmail.com>
Date: Tue, 30 Jul 2024 12:20:25 +0800
Subject: [PATCH 01/11] gh-122272: guarantee specifiers %F and %C for
 datetime.strftime to be 0-padded

---
 Lib/_pydatetime.py         | 13 +++++++++----
 Lib/test/datetimetester.py | 14 ++++++++++----
 Modules/_datetimemodule.c  | 30 +++++++++++++++++++++++++-----
 3 files changed, 44 insertions(+), 13 deletions(-)

diff --git a/Lib/_pydatetime.py b/Lib/_pydatetime.py
index 27cacb8e01ff3b..3af54d0252a793 100644
--- a/Lib/_pydatetime.py
+++ b/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)
diff --git a/Lib/test/datetimetester.py b/Lib/test/datetimetester.py
index b756413d7bf375..79e64c6f754af9 100644
--- a/Lib/test/datetimetester.py
+++ b/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
diff --git a/Modules/_datetimemodule.c b/Modules/_datetimemodule.c
index 67b49aa6ac2301..26faa17bbf0b96 100644
--- a/Modules/_datetimemodule.c
+++ b/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

From 8dc11004908b8dac26c1e55a693c15b15f4a06be Mon Sep 17 00:00:00 2001
From: Ben Hsing <blhsing@gmail.com>
Date: Tue, 30 Jul 2024 12:24:03 +0800
Subject: [PATCH 02/11] removed trailing spaces

---
 Modules/_datetimemodule.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Modules/_datetimemodule.c b/Modules/_datetimemodule.c
index 26faa17bbf0b96..baab2a7bf6f8b7 100644
--- a/Modules/_datetimemodule.c
+++ b/Modules/_datetimemodule.c
@@ -1987,7 +1987,7 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
                 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()) {

From f85cd69a9df92cc786b6aaf8823be209bc7767cb Mon Sep 17 00:00:00 2001
From: "blurb-it[bot]" <43283697+blurb-it[bot]@users.noreply.github.com>
Date: Tue, 30 Jul 2024 04:28:01 +0000
Subject: [PATCH 03/11] =?UTF-8?q?=F0=9F=93=9C=F0=9F=A4=96=20Added=20by=20b?=
 =?UTF-8?q?lurb=5Fit.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../next/Library/2024-07-30-04-27-55.gh-issue-122272.6Wwa1V.rst | 2 ++
 1 file changed, 2 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2024-07-30-04-27-55.gh-issue-122272.6Wwa1V.rst

diff --git a/Misc/NEWS.d/next/Library/2024-07-30-04-27-55.gh-issue-122272.6Wwa1V.rst b/Misc/NEWS.d/next/Library/2024-07-30-04-27-55.gh-issue-122272.6Wwa1V.rst
new file mode 100644
index 00000000000000..3279170c0f2bd6
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-07-30-04-27-55.gh-issue-122272.6Wwa1V.rst
@@ -0,0 +1,2 @@
+On some platforms such as Linux, year with century was not 0-padded when formatted by :meth:`datetime.datetime.strftime` with specifiers ``%C`` or ``%F``. The 0-padding behavior is now guaranteed.
+Patch by Ben Hsing

From 2fd709358c9da3a0f74c744ea951bbb5b0753f17 Mon Sep 17 00:00:00 2001
From: Ben Hsing <blhsing@gmail.com>
Date: Tue, 30 Jul 2024 14:06:20 +0800
Subject: [PATCH 04/11] handle %C and %F only when the C library supports them
 (at least C99)

---
 Lib/_pydatetime.py                                 | 14 +++++++++++++-
 Lib/test/datetimetester.py                         |  5 ++++-
 .../2024-07-30-04-27-55.gh-issue-122272.6Wwa1V.rst |  2 +-
 Modules/_datetimemodule.c                          | 11 ++++++++++-
 4 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/Lib/_pydatetime.py b/Lib/_pydatetime.py
index 3af54d0252a793..f15def01c35654 100644
--- a/Lib/_pydatetime.py
+++ b/Lib/_pydatetime.py
@@ -215,6 +215,17 @@ def _need_normalize_century():
             _normalize_century = True
     return _normalize_century
 
+_supports_c99 = None
+def _can_support_c99():
+    global _supports_c99
+    if _supports_c99 is None:
+        try:
+            _supports_c99 = (
+                _time.strftime("%F", (99, 1, 1, 0, 0, 0, 0, 1, 0)) != "%F")
+        except ValueError:
+            _supports_c99 = True
+    return _supports_c99
+
 # Correctly substitute for %z and %Z escapes in strftime formats.
 def _wrap_strftime(object, format, timetuple):
     # Don't call utcoffset() or tzname() unless actually needed.
@@ -274,7 +285,8 @@ def _wrap_strftime(object, format, timetuple):
                     newformat.append(Zreplace)
                 # 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():
+                elif ((ch in 'YG' or ch in 'FC' and _can_support_c99()) and
+                        object.year < 1000 and _need_normalize_century()):
                     if ch == 'G':
                         year = int(_time.strftime("%G", timetuple))
                     else:
diff --git a/Lib/test/datetimetester.py b/Lib/test/datetimetester.py
index 79e64c6f754af9..a6056dcf8d472c 100644
--- a/Lib/test/datetimetester.py
+++ b/Lib/test/datetimetester.py
@@ -1710,8 +1710,11 @@ def test_strftime_y2k(self):
             (1000, 0),
             (1970, 0),
         )
+        specifiers = 'YG'
+        if _time.strftime('%F', (99, 1, 1, 0, 0, 0, 0, 1, 0)) != '%F':
+            specifiers += 'FC'
         for year, g_offset in dataset:
-            for specifier in 'YGFC':
+            for specifier in specifiers:
                 with self.subTest(year=year, specifier=specifier):
                     d = self.theclass(year, 1, 1)
                     if specifier == 'G':
diff --git a/Misc/NEWS.d/next/Library/2024-07-30-04-27-55.gh-issue-122272.6Wwa1V.rst b/Misc/NEWS.d/next/Library/2024-07-30-04-27-55.gh-issue-122272.6Wwa1V.rst
index 3279170c0f2bd6..943010b9c16c3c 100644
--- a/Misc/NEWS.d/next/Library/2024-07-30-04-27-55.gh-issue-122272.6Wwa1V.rst
+++ b/Misc/NEWS.d/next/Library/2024-07-30-04-27-55.gh-issue-122272.6Wwa1V.rst
@@ -1,2 +1,2 @@
-On some platforms such as Linux, year with century was not 0-padded when formatted by :meth:`datetime.datetime.strftime` with specifiers ``%C`` or ``%F``. The 0-padding behavior is now guaranteed.
+On some platforms such as Linux, year with century was not 0-padded when formatted by :meth:`~.datetime.strftime` with C99-specific specifiers ``'%C'`` or ``'%F'``. The 0-padding behavior is now guaranteed when the format specifiers ``'%C'`` and ``'%F'`` are supported by the C library.
 Patch by Ben Hsing
diff --git a/Modules/_datetimemodule.c b/Modules/_datetimemodule.c
index baab2a7bf6f8b7..7818e1c178a5eb 100644
--- a/Modules/_datetimemodule.c
+++ b/Modules/_datetimemodule.c
@@ -1952,7 +1952,12 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
             ntoappend = PyBytes_GET_SIZE(freplacement);
         }
 #ifdef Py_NORMALIZE_CENTURY
-        else if (ch == 'Y' || ch == 'G' || ch == 'F' || ch == 'C') {
+        else if (ch == 'Y' || ch == 'G'
+#if __STDC_VERSION__ >= 199901L
+#define Py_STRFTIME_C99_SUPPORT
+                 || ch == 'F' || ch == 'C'
+#endif
+        ) {
             /* 0-pad year with century as necessary */
             PyObject *item = PyTuple_GET_ITEM(timetuple, 0);
             long year_long = PyLong_AsLong(item);
@@ -1982,6 +1987,7 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
                     goto Done;
                 }
             }
+#ifdef Py_STRFTIME_C99_SUPPORT
             if (ch == 'F') {
                 item = PyTuple_GET_ITEM(timetuple, 1);
                 long month = PyLong_AsLong(item);
@@ -1997,11 +2003,14 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
                                           year_long, month, day);
             }
             else {
+#endif
                 ntoappend = PyOS_snprintf(buf, sizeof(buf), "%04ld", year_long);
+#ifdef Py_STRFTIME_C99_SUPPORT
                 if (ch == 'C') {
                     ntoappend -= 2;
                 }
             }
+#endif
             ptoappend = buf;
         }
 #endif

From 8fe9521eb49d6cdd1d03c8aff7010062cdf35de8 Mon Sep 17 00:00:00 2001
From: Ben Hsing <blhsing@gmail.com>
Date: Tue, 30 Jul 2024 15:10:28 +0800
Subject: [PATCH 05/11] use autoconf instead to test if c99-specific specifiers
 are supported

---
 Modules/_datetimemodule.c |  3 +--
 configure                 | 52 +++++++++++++++++++++++++++++++++++++++
 configure.ac              | 28 +++++++++++++++++++++
 3 files changed, 81 insertions(+), 2 deletions(-)

diff --git a/Modules/_datetimemodule.c b/Modules/_datetimemodule.c
index 7818e1c178a5eb..651c1035bf9eed 100644
--- a/Modules/_datetimemodule.c
+++ b/Modules/_datetimemodule.c
@@ -1953,8 +1953,7 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
         }
 #ifdef Py_NORMALIZE_CENTURY
         else if (ch == 'Y' || ch == 'G'
-#if __STDC_VERSION__ >= 199901L
-#define Py_STRFTIME_C99_SUPPORT
+#ifdef Py_STRFTIME_C99_SUPPORT
                  || ch == 'F' || ch == 'C'
 #endif
         ) {
diff --git a/configure b/configure
index 39ab48fa4e2526..353008f72c3caf 100755
--- a/configure
+++ b/configure
@@ -26195,6 +26195,58 @@ printf "%s\n" "#define Py_NORMALIZE_CENTURY 1" >>confdefs.h
 
 fi
 
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether C99-specific strftime specifiers are supported" >&5
+printf %s "checking whether C99-specific strftime specifiers are supported... " >&6; }
+if test ${ac_cv_strftime_c99_support+y}
+then :
+  printf %s "(cached) " >&6
+else $as_nop
+
+if test "$cross_compiling" = yes
+then :
+  ac_cv_strftime_c99_support=yes
+else $as_nop
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+#include <time.h>
+#include <string.h>
+
+int main(void)
+{
+  char full_date[11];
+  struct tm date = {
+    .tm_year = -1801,
+    .tm_mon = 0,
+    .tm_mday = 1
+  };
+  if (strftime(full_date, sizeof(full_date), "%F", &date) && !strcmp(full_date, "%F")) {
+    return 1;
+  }
+  return 0;
+}
+
+_ACEOF
+if ac_fn_c_try_run "$LINENO"
+then :
+  ac_cv_strftime_c99_support=yes
+else $as_nop
+  ac_cv_strftime_c99_support=no
+fi
+rm -f core *.core core.conftest.* gmon.out bb.out conftest$ac_exeext \
+  conftest.$ac_objext conftest.beam conftest.$ac_ext
+fi
+
+fi
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $ac_cv_strftime_c99_support" >&5
+printf "%s\n" "$ac_cv_strftime_c99_support" >&6; }
+if test "$ac_cv_strftime_c99_support" = yes
+then
+
+printf "%s\n" "#define Py_STRFTIME_C99_SUPPORT 1" >>confdefs.h
+
+fi
+
 have_curses=no
 have_panel=no
 
diff --git a/configure.ac b/configure.ac
index 62ed812991fc4e..20ffec00f6285d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -6700,6 +6700,34 @@ then
   [Define if year with century should be normalized for strftime.])
 fi
 
+AC_CACHE_CHECK([whether C99-specific strftime specifiers are supported], [ac_cv_strftime_c99_support], [
+AC_RUN_IFELSE([AC_LANG_SOURCE([[
+#include <time.h>
+#include <string.h>
+
+int main(void)
+{
+  char full_date[11];
+  struct tm date = {
+    .tm_year = -1801,
+    .tm_mon = 0,
+    .tm_mday = 1
+  };
+  if (strftime(full_date, sizeof(full_date), "%F", &date) && !strcmp(full_date, "%F")) {
+    return 1;
+  }
+  return 0;
+}
+]])],
+[ac_cv_strftime_c99_support=yes],
+[ac_cv_strftime_c99_support=no],
+[ac_cv_strftime_c99_support=yes])])
+if test "$ac_cv_strftime_c99_support" = yes
+then
+  AC_DEFINE([Py_STRFTIME_C99_SUPPORT], [1],
+  [Define if C99-specific strftime specifiers are supported.])
+fi
+
 dnl check for ncursesw/ncurses and panelw/panel
 dnl NOTE: old curses is not detected.
 dnl have_curses=[no, yes]

From 4e1ea89a2bd542a42302a420d6794d79d7144c79 Mon Sep 17 00:00:00 2001
From: Ben Hsing <blhsing@gmail.com>
Date: Tue, 30 Jul 2024 15:17:26 +0800
Subject: [PATCH 06/11] generate header

---
 pyconfig.h.in | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/pyconfig.h.in b/pyconfig.h.in
index 8fbba7ed3b949e..d6b3cecbe19f82 100644
--- a/pyconfig.h.in
+++ b/pyconfig.h.in
@@ -1698,6 +1698,9 @@
 /* Define if you want to enable internal statistics gathering. */
 #undef Py_STATS
 
+/* Define if C99-specific strftime specifiers are supported. */
+#undef Py_STRFTIME_C99_SUPPORT
+
 /* The version of SunOS/Solaris as reported by `uname -r' without the dot. */
 #undef Py_SUNOS_VERSION
 

From bfd2f18648bf4137b8e72505efe0d0c9ad10ed7a Mon Sep 17 00:00:00 2001
From: Ben Hsing <blhsing@gmail.com>
Date: Tue, 30 Jul 2024 13:43:54 +0000
Subject: [PATCH 07/11] corrected logics of checks for c99 support

---
 Lib/_pydatetime.py         |  4 ++--
 Lib/test/datetimetester.py |  2 +-
 configure                  | 10 +++++-----
 configure.ac               | 10 +++++-----
 4 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/Lib/_pydatetime.py b/Lib/_pydatetime.py
index f15def01c35654..b609583944be57 100644
--- a/Lib/_pydatetime.py
+++ b/Lib/_pydatetime.py
@@ -221,9 +221,9 @@ def _can_support_c99():
     if _supports_c99 is None:
         try:
             _supports_c99 = (
-                _time.strftime("%F", (99, 1, 1, 0, 0, 0, 0, 1, 0)) != "%F")
+                _time.strftime("%F", (1900, 1, 1, 0, 0, 0, 0, 1, 0)) == "1900-01-01")
         except ValueError:
-            _supports_c99 = True
+            pass
     return _supports_c99
 
 # Correctly substitute for %z and %Z escapes in strftime formats.
diff --git a/Lib/test/datetimetester.py b/Lib/test/datetimetester.py
index a6056dcf8d472c..e7adea0af5526a 100644
--- a/Lib/test/datetimetester.py
+++ b/Lib/test/datetimetester.py
@@ -1711,7 +1711,7 @@ def test_strftime_y2k(self):
             (1970, 0),
         )
         specifiers = 'YG'
-        if _time.strftime('%F', (99, 1, 1, 0, 0, 0, 0, 1, 0)) != '%F':
+        if _time.strftime('%F', (1900, 1, 1, 0, 0, 0, 0, 1, 0)) == '1900-01-01':
             specifiers += 'FC'
         for year, g_offset in dataset:
             for specifier in specifiers:
diff --git a/configure b/configure
index 353008f72c3caf..f9da540dc09fb7 100755
--- a/configure
+++ b/configure
@@ -26204,7 +26204,7 @@ else $as_nop
 
 if test "$cross_compiling" = yes
 then :
-  ac_cv_strftime_c99_support=yes
+  ac_cv_strftime_c99_support=no
 else $as_nop
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
@@ -26216,14 +26216,14 @@ int main(void)
 {
   char full_date[11];
   struct tm date = {
-    .tm_year = -1801,
+    .tm_year = 0,
     .tm_mon = 0,
     .tm_mday = 1
   };
-  if (strftime(full_date, sizeof(full_date), "%F", &date) && !strcmp(full_date, "%F")) {
-    return 1;
+  if (strftime(full_date, sizeof(full_date), "%F", &date) && !strcmp(full_date, "1900-01-01")) {
+    return 0;
   }
-  return 0;
+  return 1;
 }
 
 _ACEOF
diff --git a/configure.ac b/configure.ac
index 20ffec00f6285d..0d3455dea9b0a5 100644
--- a/configure.ac
+++ b/configure.ac
@@ -6709,19 +6709,19 @@ int main(void)
 {
   char full_date[11];
   struct tm date = {
-    .tm_year = -1801,
+    .tm_year = 0,
     .tm_mon = 0,
     .tm_mday = 1
   };
-  if (strftime(full_date, sizeof(full_date), "%F", &date) && !strcmp(full_date, "%F")) {
-    return 1;
+  if (strftime(full_date, sizeof(full_date), "%F", &date) && !strcmp(full_date, "1900-01-01")) {
+    return 0;
   }
-  return 0;
+  return 1;
 }
 ]])],
 [ac_cv_strftime_c99_support=yes],
 [ac_cv_strftime_c99_support=no],
-[ac_cv_strftime_c99_support=yes])])
+[ac_cv_strftime_c99_support=no])])
 if test "$ac_cv_strftime_c99_support" = yes
 then
   AC_DEFINE([Py_STRFTIME_C99_SUPPORT], [1],

From fd8dd3099de4a4817bfabd8a88205e7e17aef172 Mon Sep 17 00:00:00 2001
From: Ben Hsing <blhsing@gmail.com>
Date: Wed, 31 Jul 2024 09:03:41 +0800
Subject: [PATCH 08/11] allocate 6 more bytes for the formatted date buffer
 only when %F is supported

---
 Modules/_datetimemodule.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/Modules/_datetimemodule.c b/Modules/_datetimemodule.c
index 651c1035bf9eed..25196e6d7dabe8 100644
--- a/Modules/_datetimemodule.c
+++ b/Modules/_datetimemodule.c
@@ -1852,10 +1852,13 @@ 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.
-     * Adding 6 just to accomodate %F with dashes, 2-digit month and day.
-     */
-    char buf[SIZEOF_LONG*5/2+2+6];
+    /* Buffer of maximum size of formatted year permitted by long. */
+    char buf[SIZEOF_LONG * 5 / 2 + 2
+#ifdef Py_STRFTIME_C99_SUPPORT
+    /* Need 6 more to accomodate dashes, 2-digit month and day for %F. */
+             + 6
+#endif
+    ];
 #endif
 
     assert(object && format && timetuple);

From 3e36832fc40ccab7de986ed91b39d030474517c3 Mon Sep 17 00:00:00 2001
From: Ben Hsing <blhsing@gmail.com>
Date: Fri, 16 Aug 2024 17:20:27 +0800
Subject: [PATCH 09/11] pass through month and day to time.strftime for %F;
 made _supports_c99 return False on error

---
 Lib/_pydatetime.py        |  2 +-
 Modules/_datetimemodule.c | 30 +++++++++---------------------
 2 files changed, 10 insertions(+), 22 deletions(-)

diff --git a/Lib/_pydatetime.py b/Lib/_pydatetime.py
index b609583944be57..e1773cd52585d9 100644
--- a/Lib/_pydatetime.py
+++ b/Lib/_pydatetime.py
@@ -223,7 +223,7 @@ def _can_support_c99():
             _supports_c99 = (
                 _time.strftime("%F", (1900, 1, 1, 0, 0, 0, 0, 1, 0)) == "1900-01-01")
         except ValueError:
-            pass
+            return False
     return _supports_c99
 
 # Correctly substitute for %z and %Z escapes in strftime formats.
diff --git a/Modules/_datetimemodule.c b/Modules/_datetimemodule.c
index 25196e6d7dabe8..77d51ca521375b 100644
--- a/Modules/_datetimemodule.c
+++ b/Modules/_datetimemodule.c
@@ -1961,9 +1961,11 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
 #endif
         ) {
             /* 0-pad year with century as necessary */
-            PyObject *item = PyTuple_GET_ITEM(timetuple, 0);
+            PyObject *item = PyTuple_GetItem(timetuple, 0);
+            if (item == NULL) {
+                goto Done;
+            }
             long year_long = PyLong_AsLong(item);
-
             if (year_long == -1 && PyErr_Occurred()) {
                 goto Done;
             }
@@ -1989,28 +1991,14 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
                     goto Done;
                 }
             }
+            ntoappend = PyOS_snprintf(buf, sizeof(buf),
 #ifdef Py_STRFTIME_C99_SUPPORT
-            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 {
+                                      ch == 'F' ? "%04ld-%%m-%%d" :
 #endif
-                ntoappend = PyOS_snprintf(buf, sizeof(buf), "%04ld", year_long);
+                                      "%04ld", year_long);
 #ifdef Py_STRFTIME_C99_SUPPORT
-                if (ch == 'C') {
-                    ntoappend -= 2;
-                }
+            if (ch == 'C') {
+                ntoappend -= 2;
             }
 #endif
             ptoappend = buf;

From 3530288d42ceffc9222b9ae3983884dd7261a6bb Mon Sep 17 00:00:00 2001
From: Ben Hsing <blhsing@gmail.com>
Date: Thu, 22 Aug 2024 16:46:12 +0800
Subject: [PATCH 10/11] validate timetuple as a tuple; cache result of
 _can_support_c99 upon error

---
 Lib/_pydatetime.py        | 2 +-
 Modules/_datetimemodule.c | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/Lib/_pydatetime.py b/Lib/_pydatetime.py
index e1773cd52585d9..78432d46506be8 100644
--- a/Lib/_pydatetime.py
+++ b/Lib/_pydatetime.py
@@ -223,7 +223,7 @@ def _can_support_c99():
             _supports_c99 = (
                 _time.strftime("%F", (1900, 1, 1, 0, 0, 0, 0, 1, 0)) == "1900-01-01")
         except ValueError:
-            return False
+            _supports_c99 = False
     return _supports_c99
 
 # Correctly substitute for %z and %Z escapes in strftime formats.
diff --git a/Modules/_datetimemodule.c b/Modules/_datetimemodule.c
index 77d51ca521375b..6259a051a41843 100644
--- a/Modules/_datetimemodule.c
+++ b/Modules/_datetimemodule.c
@@ -1961,6 +1961,9 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
 #endif
         ) {
             /* 0-pad year with century as necessary */
+            if (!PyTuple_Check(timetuple)) {
+                goto Done;
+            }
             PyObject *item = PyTuple_GetItem(timetuple, 0);
             if (item == NULL) {
                 goto Done;

From c9c51d766f6ad37ea7ac98868fb4509b9dd469ee Mon Sep 17 00:00:00 2001
From: Ben Hsing <blhsing@gmail.com>
Date: Fri, 23 Aug 2024 17:33:44 +0800
Subject: [PATCH 11/11] use PySequence_GetItem instead of PyTuple_GetItem for
 better error handling

---
 Modules/_datetimemodule.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/Modules/_datetimemodule.c b/Modules/_datetimemodule.c
index 6259a051a41843..79314e06c82f69 100644
--- a/Modules/_datetimemodule.c
+++ b/Modules/_datetimemodule.c
@@ -1961,14 +1961,12 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
 #endif
         ) {
             /* 0-pad year with century as necessary */
-            if (!PyTuple_Check(timetuple)) {
-                goto Done;
-            }
-            PyObject *item = PyTuple_GetItem(timetuple, 0);
+            PyObject *item = PySequence_GetItem(timetuple, 0);
             if (item == NULL) {
                 goto Done;
             }
             long year_long = PyLong_AsLong(item);
+            Py_DECREF(item);
             if (year_long == -1 && PyErr_Occurred()) {
                 goto Done;
             }