gh-137165: Add non-zero-padded Windows support for datetime.strftime

Lib/_pydatetime.py

@@ -213,6 +213,11 @@ def _need_normalize_century():
             _normalize_century = True
     return _normalize_century
 
+def _make_dash_replacement(ch, timetuple):
+    fmt = '%' + ch
+    val = _time.strftime(fmt, timetuple)
+    return val.lstrip('0') or '0'
+
 # 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.
@@ -284,6 +289,16 @@ def _wrap_strftime(object, format, timetuple):
                         push('{:04}'.format(year))
                         if ch == 'F':
                             push('-{:02}-{:02}'.format(*timetuple[1:3]))
+                elif ch == '-':
+                    if i < n:
+                        next_ch = format[i]
+                        i += 1
+                        if sys.platform.startswith('win') or sys.platform.startswith('android'):
+                            push(_make_dash_replacement(next_ch, timetuple))
+                        else:
+                            push('%-' + next_ch)
+                    else:
+                        push('%-')
                 else:
                     push('%')
                     push(ch)

Lib/test/datetimetester.py

@@ -14,6 +14,7 @@
 import textwrap
 import unittest
 import warnings
+import platform
 
 from array import array
 
@@ -1588,6 +1589,15 @@ def test_strftime(self):
         self.assertEqual(t.strftime(""), "") # SF bug #761337
         self.assertEqual(t.strftime('x'*1000), 'x'*1000) # SF bug #1556784
 
+        # SF bug #137165
+        if platform.system() == 'Darwin':
+            self.assertEqual(t.strftime("m:%-m d:%-d y:%-y"), "m:3 d:2 y:05")
+        elif platform.system() == 'Windows':
+            self.assertEqual(t.strftime("m:%#m d:%#d y:%#y"), "m:3 d:2 y:5")
+            self.assertEqual(t.strftime("m:%-m d:%-d y:%-y"), "m:3 d:2 y:5")
+        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
         self.assertRaises(TypeError, t.strftime, 42) # arg wrong type
@@ -3890,6 +3900,11 @@ def test_strftime(self):
         # A naive object replaces %z, %:z and %Z with empty strings.
         self.assertEqual(t.strftime("'%z' '%:z' '%Z'"), "'' '' ''")
 
+        # SF bug #137165
+        self.assertEqual(t.strftime('%-H %-M %-S %f'), "1 2 3 000004")
+        if platform.system() == 'Windows':
+            self.assertEqual(t.strftime('%#H %#M %#S %f'), "1 2 3 000004")
+
         # bpo-34482: Check that surrogates don't cause a crash.
         try:
             t.strftime('%H\ud800%M')

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

@@ -1856,6 +1856,39 @@ make_freplacement(PyObject *object)
     return PyUnicode_FromString(freplacement);
 }
 
+#if defined(MS_WINDOWS) || defined(__ANDROID__)
+static PyObject *
+make_dash_replacement(PyObject *object, Py_UCS4 ch, PyObject *timetuple)
+{
+    PyObject *strftime = PyImport_ImportModuleAttrString("time", "strftime");
+    if (!strftime) {
+        return NULL;
+    }
+
+    char fmt[3] = {'%', (char)ch, 0};
+    PyObject *fmt_obj = PyUnicode_FromString(fmt);
+    if (!fmt_obj) {
+        Py_DECREF(strftime);
+        return NULL;
+    }
+
+    PyObject *res = PyObject_CallFunctionObjArgs(strftime, fmt_obj, timetuple, NULL);
+    Py_DECREF(fmt_obj);
+    Py_DECREF(strftime);
+    if (!res) {
+        return NULL;
+    }
+
+    PyObject *stripped = PyObject_CallMethod(res, "lstrip", "s", "0");
+    Py_DECREF(res);
+    if (!stripped) {
+        return NULL;
+    }
+
+    return stripped;
+}
+#endif
+
 /* I sure don't want to reproduce the strftime code from the time module,
  * so this imports the module and calls it.  All the hair is due to
  * giving special meanings to the %z, %:z, %Z and %f format codes via a
@@ -2002,6 +2035,17 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
             }
             continue;
         }
+        #if defined(MS_WINDOWS) || defined(__ANDROID__)
+        /* non-0-pad Windows support */
+        else if (ch == '-' && i < flen) {
+            Py_UCS4 next_ch = PyUnicode_READ_CHAR(format, i);
+            i++;
+            replacement = make_dash_replacement(object, next_ch, timetuple);
+            if (replacement == NULL) {
+                goto Error;
+            }
+        }
+        #endif
         else {
             /* percent followed by something else */
             continue;