Keep IDLE from displaying spurious SystemExit tracebacks

when running scripts that terminated by raising SystemExit
(i.e. unittest and turtledemo).

Lib/idlelib/run.py

@@ -301,11 +301,14 @@ class Executive(object):
                 exec code in self.locals
             finally:
                 interruptable = False
+        except SystemExit:
+            # Scripts that raise SystemExit should just
+            # return to the interactive prompt
+            pass
         except:
             self.usr_exc_info = sys.exc_info()
             if quitting:
                 exit()
-            # even print a user code SystemExit exception, continue
             print_exception()
             jit = self.rpchandler.console.getvar("<<toggle-jit-stack-viewer>>")
             if jit:

Misc/NEWS

@@ -205,6 +205,9 @@ Library
 - Issue #7358: cStringIO.StringIO now supports writing to and reading from
   a stream larger than 2 GiB on 64-bit systems.
 
+- IDLE was displaying spurious SystemExit tracebacks when running scripts
+  that terminated by raising SystemExit (i.e. unittest and turtledemo).
+
 - Issue #10355: In SpooledTemporaryFile class mode and name properties and
   xreadlines method now work for unrolled files.  encoding and newlines
   properties now removed as they have no sense and always produced