# HG changeset patch
# User Antoine Pitrou <antoine@p.i.t.r.o.u.net>
# Date 1229460178 -3600

diff -r d2d6e0601fb7 -r 92050334323e Lib/test/test_traceback.py
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -239,6 +239,26 @@
         self.check_zero_div(blocks[0])
         self.assert_('inner_raise() # Marker' in blocks[2])
 
+    def test_cause_and_context(self):
+        # When both a cause and a context are set, only the cause should be
+        # displayed and the context should be muted.
+        def inner_raise():
+            try:
+                self.zero_div()
+            except ZeroDivisionError as _e:
+                e = _e
+            try:
+                xyzzy
+            except NameError:
+                raise KeyError from e
+        def outer_raise():
+            inner_raise() # Marker
+        blocks = boundaries.split(self.get_report(outer_raise))
+        self.assertEquals(len(blocks), 3)
+        self.assertEquals(blocks[1], cause_message)
+        self.check_zero_div(blocks[0])
+        self.assert_('inner_raise() # Marker' in blocks[2])
+
     def test_cause_recursive(self):
         def inner_raise():
             try:
diff -r d2d6e0601fb7 -r 92050334323e Lib/traceback.py
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -120,13 +120,14 @@
     seen.add(exc)
     its = []
     cause = exc.__cause__
-    context = exc.__context__
     if cause is not None and cause not in seen:
         its.append(_iter_chain(cause, None, seen))
         its.append([(_cause_message, None)])
-    if context is not None and context is not cause and context not in seen:
-        its.append(_iter_chain(context, None, seen))
-        its.append([(_context_message, None)])
+    else:
+        context = exc.__context__
+        if context is not None and context not in seen:
+            its.append(_iter_chain(context, None, seen))
+            its.append([(_context_message, None)])
     its.append([(exc, custom_tb or exc.__traceback__)])
     # itertools.chain is in an extension module and may be unavailable
     for it in its:
diff -r d2d6e0601fb7 -r 92050334323e Python/pythonrun.c
--- a/Python/pythonrun.c
+++ b/Python/pythonrun.c
@@ -1477,7 +1477,7 @@
 						cause_message, f);
 				}
 			}
-			if (context) {
+			else if (context) {
 				res = PySet_Contains(seen, context);
 				if (res == -1)
 					PyErr_Clear();