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

2 files changed, 13 insertions, 2 deletions

diff --git a/Lib/test/test_tcl.py b/Lib/test/test_tcl.py
index fa170ef58d..26e294ce13 100644
--- a/Lib/test/test_tcl.py
+++ b/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()
diff --git a/Modules/_tkinter.c b/Modules/_tkinter.c
index 93e7edc546..6e89f2f9c3 100644
--- a/Modules/_tkinter.c
+++ b/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);