make _tkinter._flatten check the result of PySequence_Size for errors #3880

Lib/test/test_tcl.py

@@ -2,10 +2,19 @@
 
 import unittest
 import os
+import _tkinter
 from test import test_support
 from Tkinter import Tcl
 from _tkinter import TclError
 
+
+class TkinterTest(unittest.TestCase):
+
+    def testFlattenLen(self):
+        # flatten(<object with no length>)
+        self.assertRaises(TypeError, _tkinter._flatten, True)
+
+
 class TclTest(unittest.TestCase):
 
     def setUp(self):
@@ -151,7 +160,7 @@ class TclTest(unittest.TestCase):
                 os.environ['DISPLAY'] = old_display
 
 def test_main():
-    test_support.run_unittest(TclTest)
+    test_support.run_unittest(TclTest, TkinterTest)
 
 if __name__ == "__main__":
     test_main()

Modules/_tkinter.c

@@ -2908,7 +2908,9 @@ Tkinter_Flatten(PyObject* self, PyObject* args)
 		return NULL;
 
 	context.maxsize = PySequence_Size(item);
-	if (context.maxsize <= 0)
+	if (context.maxsize < 0)
+		return NULL;
+	if (context.maxsize == 0)
 		return PyTuple_New(0);
 	
 	context.tuple = PyTuple_New(context.maxsize);