Handle KeyboardInterrupt consistently in python scripts

git_nav_downstream.py

 #!/usr/bin/env python
 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """
 Checks out a downstream branch from the currently checked out branch. If there
 is more than one downstream branch, then this script will prompt you to select
 which branch.
 """
@@ skipping 16 matching lines @@
   cur = current_branch()
   if cur == 'HEAD':
     def _upfn(b):
       parent = upstream(b)
       if parent:
         return hash_one(parent)
     upfn = _upfn
     cur = hash_one(cur)
   downstreams = [b for b in branches() if upfn(b) == cur]
   if not downstreams:
-    return "No downstream branches"
+    print "No downstream branches"
+    return 1
   elif len(downstreams) == 1:
     run('checkout', downstreams[0], stdout=sys.stdout, stderr=sys.stderr)
   else:
     high = len(downstreams) - 1
     while True:
       print "Please select a downstream branch"
       for i, b in enumerate(downstreams):
         print "  %d. %s" % (i, b)
       prompt = "Selection (0-%d)[0]: " % high
       r = opts.pick
       if r:
         print prompt + r
       else:
         r = raw_input(prompt).strip() or '0'
       if not r.isdigit() or (0 > int(r) > high):
         print "Invalid choice."
       else:
         run('checkout', downstreams[int(r)], stdout=sys.stdout,
             stderr=sys.stderr)
         break
+  return 0
 
 
 if __name__ == '__main__':
   try:
     sys.exit(main(sys.argv[1:]))
   except KeyboardInterrupt:
-    pass
+    sys.stderr.write('interrupted\n')
+    sys.exit(1)