diff -r aa214fefbdc1 Lib/test/test_raise.py
--- a/Lib/test/test_raise.py	Sat Jan 28 20:33:52 2012 -0500
+++ b/Lib/test/test_raise.py	Sat Jan 28 23:23:44 2012 -0800
@@ -77,6 +77,16 @@ class TestRaise(unittest.TestCase):
                 nested_reraise()
         self.assertRaises(TypeError, reraise)
 
+    def test_raise_from_None(self):
+        try:
+            try:
+                raise TypeError("foo")
+            except:
+                raise ValueError() from None
+        except ValueError as e:
+            self.assertTrue(isinstance(e.__context__, TypeError))
+            self.assertTrue(e.__cause__)
+
     def test_with_reraise1(self):
         def reraise():
             try:
diff -r aa214fefbdc1 Python/ceval.c
--- a/Python/ceval.c	Sat Jan 28 20:33:52 2012 -0500
+++ b/Python/ceval.c	Sat Jan 28 23:23:44 2012 -0800
@@ -3576,6 +3576,11 @@ do_raise(PyObject *exc, PyObject *cause)
         else if (PyExceptionInstance_Check(cause)) {
             fixed_cause = cause;
         }
+        else if (cause == Py_None) {
+            fixed_cause = Py_True;
+            Py_INCREF(Py_True);
+            Py_DECREF(cause);
+        }
         else {
             PyErr_SetString(PyExc_TypeError,
                             "exception causes must derive from "
diff -r aa214fefbdc1 Python/pythonrun.c
--- a/Python/pythonrun.c	Sat Jan 28 20:33:52 2012 -0500
+++ b/Python/pythonrun.c	Sat Jan 28 23:23:44 2012 -0800
@@ -1691,7 +1691,11 @@ print_exception_recursive(PyObject *f, P
         else if (PyExceptionInstance_Check(value)) {
             cause = PyException_GetCause(value);
             context = PyException_GetContext(value);
-            if (cause) {
+            if (cause && cause == Py_True) {
+                /* print neither cause nor context */
+                ;
+            }
+            else if (cause) {
                 res = PySet_Contains(seen, cause);
                 if (res == -1)
                     PyErr_Clear();