gh-137165: Add non-zero-padded Windows support

Author: marat

Lib/test/datetimetester.py

@@ -1587,6 +1587,11 @@ def test_strftime(self):
         self.assertEqual(t.strftime("m:%m d:%d y:%y"), "m:03 d:02 y:05")
         self.assertEqual(t.strftime(""), "") # SF bug #761337
         self.assertEqual(t.strftime('x'*1000), 'x'*1000) # SF bug #1556784
+        self.assertEqual(t.strftime("m:%-m d:%-d"), "m:3 d:2") # SF bug #137165
+        if sys.platform.startswith('darwin'): # SF bug #137165
+            self.assertEqual(t.strftime("m:%-m d:%-d y:%-y"), "m:3 d:2 y:05")
+        else:
+            self.assertEqual(t.strftime("m:%-m d:%-d y:%-y"), "m:3 d:2 y:5")
 
         self.assertRaises(TypeError, t.strftime) # needs an arg
         self.assertRaises(TypeError, t.strftime, "one", "two") # too many args
@@ -3889,6 +3894,7 @@ def test_strftime(self):
         self.assertEqual(t.strftime('%H %M %S %f'), "01 02 03 000004")
         # A naive object replaces %z, %:z and %Z with empty strings.
         self.assertEqual(t.strftime("'%z' '%:z' '%Z'"), "'' '' ''")
+        self.assertEqual(t.strftime('%-H %-M %-S %f'), "1 2 3 000004") # SF bug #137165
 
         # bpo-34482: Check that surrogates don't cause a crash.
         try:

Misc/NEWS.d/next/Library/2025-09-16-15-36-18.gh-issue-137165.AclPcn.rst

@@ -0,0 +1,2 @@
+Add support for Windows non-zero-padded formatting directives in
+:func:`datetime.datetime.strftime` (e.g., ``"m:%-m d:%-d y:%-y"``).

Modules/_datetimemodule.c

@@ -2002,6 +2002,21 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
             }
             continue;
         }
+        #ifdef MS_WINDOWS
+        /* non-0-pad Windows support */
+        else if (ch == '-' && i < flen) {
+            Py_UCS4 next_ch = PyUnicode_READ_CHAR(format, i);
+            if (strchr("dHImMSUwWyY", next_ch) != NULL) {
+                i++;
+                replacement = PyUnicode_FromFormat("%s%c", "%#", next_ch);
+                if (replacement == NULL) {
+                    goto Error;
+                }
+            } else {
+                continue;
+            }
+        }
+        #endif
         else {
             /* percent followed by something else */
             continue;