Correct one of the "MemoryError oddities":

the traceback would grow each time a MemoryError is raised.

Lib/test/test_exceptions.py

@@ -596,6 +596,24 @@ class ExceptionTests(unittest.TestCase):
                          "Exception ValueError: ValueError() "
                          "in <class 'KeyError'> ignored\n")
 
+
+    def test_MemoryError(self):
+        # PyErr_NoMemory always raises the same exception instance.
+        # Check that the traceback is not doubled.
+        import traceback
+        def raiseMemError():
+            try:
+                "a" * (sys.maxsize // 2)
+            except MemoryError as e:
+                tb = e.__traceback__
+            else:
+                self.fail("Should have raises a MemoryError")
+            return traceback.format_tb(tb)
+
+        tb1 = raiseMemError()
+        tb2 = raiseMemError()
+        self.assertEqual(tb1, tb2)
+
 def test_main():
     run_unittest(ExceptionTests)
 

Python/errors.c

@@ -321,7 +321,17 @@ PyErr_NoMemory(void)
 
 	/* raise the pre-allocated instance if it still exists */
 	if (PyExc_MemoryErrorInst)
+	{
+		/* Clear the previous traceback, otherwise it will be appended
+		 * to the current one.
+		 *
+		 * The following statement is not likely to raise any error;
+		 * if it does, we simply discard it.
+		 */
+		PyException_SetTraceback(PyExc_MemoryErrorInst, Py_None);
+
 		PyErr_SetObject(PyExc_MemoryError, PyExc_MemoryErrorInst);
+	}
 	else
 		/* this will probably fail since there's no memory and hee,
 		   hee, we have to instantiate this class