Issue #3129: Trailing digits in format string are no longer ignored.

Lib/test/test_struct.py

@@ -443,7 +443,7 @@ def test_pack_into(self):
 
         # Test bogus offset (issue 3694)
         sb = small_buf
-        self.assertRaises(TypeError, struct.pack_into, b'1', sb, None)
+        self.assertRaises(TypeError, struct.pack_into, b'', sb, None)
 
     def test_pack_into_fn(self):
         test_string = b'Reykjavik rocks, eow!'
@@ -510,6 +510,32 @@ def test_bool(self):
         def test_crasher(self):
             self.assertRaises(MemoryError, struct.pack, "357913941b", "a")
 
+    def test_trailing_counter(self):
+        store = array.array('b', b' '*100)
+
+        # format lists containing only count spec should result in an error
+        self.assertRaises(struct.error, struct.pack, '12345')
+        self.assertRaises(struct.error, struct.unpack, '12345', '')
+        self.assertRaises(struct.error, struct.pack_into, '12345', store, 0)
+        self.assertRaises(struct.error, struct.unpack_from, '12345', store, 0)
+
+        # Format lists with trailing count spec should result in an error
+        self.assertRaises(struct.error, struct.pack, 'c12345', 'x')
+        self.assertRaises(struct.error, struct.unpack, 'c12345', 'x')
+        self.assertRaises(struct.error, struct.pack_into, 'c12345', store, 0,
+                           'x')
+        self.assertRaises(struct.error, struct.unpack_from, 'c12345', store,
+                           0)
+
+        # Mixed format tests
+        self.assertRaises(struct.error, struct.pack, '14s42', 'spam and eggs')
+        self.assertRaises(struct.error, struct.unpack, '14s42',
+                          'spam and eggs')
+        self.assertRaises(struct.error, struct.pack_into, '14s42', store, 0,
+                          'spam and eggs')
+        self.assertRaises(struct.error, struct.unpack_from, '14s42', store, 0)
+
+
 
 def test_main():
     run_unittest(StructTest)

Misc/NEWS

@@ -1283,6 +1283,10 @@ Library
 Extension Modules
 -----------------
 
+- Issue #3129: Trailing digits in format string are no longer ignored.
+  For example, "1" or "ilib123" are now invalid formats and cause 
+  ``struct.error`` to be raised.
+
 - Issue #7384: If the system readline library is linked against ncurses,
   the curses module must be linked against ncurses as well. Otherwise it
   is not safe to load both the readline and curses modules in an application.

Modules/_struct.c

@@ -1195,8 +1195,11 @@ prepare_s(PyStructObject *self)
                 }
                 num = x;
             }
-            if (c == '\0')
+            if (c == '\0') {
-                break;
+                PyErr_SetString(StructError,
+                                "repeat count given without format specifier");
+                return -1;
+            }
         }
         else
             num = 1;