Unify behavior of unsupported %-format specifiers

Author: marat

Lib/_pydatetime.py

@@ -214,9 +214,6 @@ def _need_normalize_century():
     return _normalize_century
 
 def _make_dash_replacement(ch, timetuple):
-    if ch not in 'dmHIMSjUWVy':
-        raise ValueError('invalid format string')
-
     fmt = '%' + ch
     val = _time.strftime(fmt, timetuple)
     return val.lstrip('0') or '0'
@@ -296,10 +293,13 @@ def _wrap_strftime(object, format, timetuple):
                     if i < n:
                         next_ch = format[i]
                         i += 1
-                        if sys.platform in ['win32', 'android']:
-                            push(_make_dash_replacement(next_ch, timetuple))
+                        if next_ch not in 'dmHIMSjUWVy':
+                            push('%%-' + next_ch)
                         else:
-                            push('%-' + next_ch)
+                            if sys.platform in ['win32', 'android']:
+                                push(_make_dash_replacement(next_ch, timetuple))
+                            else:
+                                push('%-' + next_ch)
                     else:
                         push('%-')
                 else:

Lib/test/datetimetester.py

@@ -1600,20 +1600,10 @@ def test_strftime(self):
 
         self.assertEqual(t.strftime("%-j. %-U. %-W. %-V."), "61. 9. 9. 9.")
 
-        if platform.system() in ("Windows", "Android"):
-            # invalid %-format specifiers must raise ValueError
-            self.assertRaises(ValueError, t.strftime, "%-1")
-            self.assertRaises(ValueError, t.strftime, "%--")
-            self.assertRaises(ValueError, t.strftime, "%-p")
-            self.assertRaises(ValueError, t.strftime, "%-#")
-        elif platform.system() in ("Darwin", "iOS", "FreeBSD"):
-            self.assertEqual(t.strftime("%-1"), "1")
-            self.assertEqual(t.strftime("%--"), "-")
-            self.assertEqual(t.strftime("%-#"), "#")
-        else:
-            self.assertEqual(t.strftime("%-1"), "%-1")
-            self.assertEqual(t.strftime("%--"), "%--")
-            self.assertEqual(t.strftime("%-#"), "%-#")
+        # unsupported %-format specifiers are passed through unchanged.
+        self.assertEqual(t.strftime("%-1"), "%-1")
+        self.assertEqual(t.strftime("%--"), "%--")
+        self.assertEqual(t.strftime("%-#"), "%-#")
 
         self.assertRaises(TypeError, t.strftime) # needs an arg
         self.assertRaises(TypeError, t.strftime, "one", "two") # too many args

Modules/_datetimemodule.c

@@ -2052,24 +2052,31 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
             }
             continue;
         }
-        #if defined(MS_WINDOWS) || defined(__ANDROID__)
         /* non-0-pad Windows and Android support */
         else if (ch == '-' && i < flen) {
             Py_UCS4 next_ch = PyUnicode_READ_CHAR(format, i);
+            i++;
+
             if (strchr("dmHIMSjUWVy", (int)next_ch) == NULL) {
-                PyErr_SetString(PyExc_ValueError, "invalid format string");
-                goto Error;
+                replacement = PyUnicode_FromFormat("%%%%-%c", (char)next_ch);
+                if (replacement == NULL) {
+                    goto Error;
+                }
             }
-            i++;
+            else {
+                #if defined(MS_WINDOWS) || defined(__ANDROID__)
+                Py_XDECREF(dash_replacement);
 
-            Py_XDECREF(dash_replacement);
-            dash_replacement = make_dash_replacement(object, next_ch, timetuple);
-            if (dash_replacement == NULL) {
-                goto Error;
+                dash_replacement = make_dash_replacement(object, next_ch, timetuple);
+                if (dash_replacement == NULL) {
+                    goto Error;
+                }
+                replacement = dash_replacement;
+                #else
+                continue;
+                #endif
             }
-            replacement = dash_replacement;
         }
-        #endif
         else {
             /* percent followed by something else */
             continue;