Add check for invalid specifiers

Author: marat

Lib/_pydatetime.py

@@ -214,6 +214,9 @@ 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'

Lib/test/datetimetester.py

@@ -1591,15 +1591,30 @@ def test_strftime(self):
         self.assertEqual(t.strftime('x'*1000), 'x'*1000) # SF bug #1556784
 
         # See gh-137165
-        if platform.system() in ('Darwin', 'iOS', 'FreeBSD'):
+        if platform.system() in ("Darwin", "iOS", "FreeBSD"):
             self.assertEqual(t.strftime("m:%-m d:%-d y:%-y"), "m:3 d:2 y:05")
         else:
-            if platform.system() == 'Windows':
+            if 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")
 
         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("%-#"), "%-#")
+
         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

Modules/_datetimemodule.c

@@ -2056,6 +2056,10 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
         /* non-0-pad Windows and Android support */
         else if (ch == '-' && i < flen) {
             Py_UCS4 next_ch = PyUnicode_READ_CHAR(format, i);
+            if (strchr("dmHIMSjUWVy", (int)next_ch) == NULL) {
+                PyErr_SetString(PyExc_ValueError, "invalid format string");
+                goto Error;
+            }
             i++;
 
             Py_XDECREF(dash_replacement);