Fix 0 seconds/minutes strip and update docs

Author: marat

Doc/library/datetime.rst

@@ -2764,8 +2764,9 @@ Notes:
 (9)
    When used with the :meth:`~.datetime.strftime` method, the leading zero is optional
    for formats ``%d``, ``%m``, ``%H``, ``%I``, ``%M``, ``%S``, ``%j``, ``%U``,
-   ``%W``, ``%V`` and ``%y`` (except that on Apple platforms, ``%y`` always produces a leading zero).
-   Use the ``%-`` flag to produce non-zero-padded output (e.g. ``%-d``).
+   ``%W``, ``%V`` and ``%y`` (except that on Apple platforms, ``%y`` always produces
+   a leading zero). Use the ``%-`` flag to produce non-zero-padded output
+   (for example, ``%-d``).
 
 (10)
    When used with the :meth:`~.datetime.strptime` method, the leading zero is optional

Lib/test/datetimetester.py

@@ -1589,7 +1589,7 @@ 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
+        # See gh-137165
         if platform.system() in ('Darwin', 'iOS'):
             self.assertEqual(t.strftime("m:%-m d:%-d y:%-y"), "m:3 d:2 y:05")
         else:
@@ -3901,11 +3901,14 @@ 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
+        # See gh-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")
 
+        t_zero = self.theclass(0, 0, 0, 4)
+        self.assertEqual(t_zero.strftime('%-H %-M %-S %f'), "0 0 0 000004")
+
         # bpo-34482: Check that surrogates don't cause a crash.
         try:
             t.strftime('%H\ud800%M')

Modules/_datetimemodule.c

@@ -1885,6 +1885,10 @@ make_dash_replacement(PyObject *object, Py_UCS4 ch, PyObject *timetuple)
         goto error;
     }
 
+    if (PyUnicode_GET_LENGTH(stripped) == 0) {
+        stripped = PyUnicode_FromString("0");
+    }
+
     Py_DECREF(fmt_obj);
     Py_DECREF(strftime);
     Py_DECREF(res);