whisper-update takes values from stdin (#318)

- also mention this in --help text

bin/whisper-update.py

@@ -16,16 +16,22 @@
 now = int(time.time())
 
 option_parser = optparse.OptionParser(
-    usage='''%prog [options] path timestamp:value [timestamp:value]*''')
+  usage='''%prog [options] path [timestamp:value]*
+
+  If no values are passed as arguments, they are read one-per-line from stdin.''')
 
 (options, args) = option_parser.parse_args()
 
-if len(args) < 2:
+if not args:
   option_parser.print_help()
   sys.exit(1)
 
 path = args[0]
-datapoint_strings = args[1:]
+if len(args) >= 2:
+  datapoint_strings = args[1:]
+else:
+  # no argv values, so read from stdin
+  datapoint_strings = sys.stdin
 datapoint_strings = [point.replace('N:', '%d:' % now)
                      for point in datapoint_strings]
 datapoints = [tuple(point.split(':')) for point in datapoint_strings]