code: def sign(mv):
      
      md5 = hashlib.md5()
      update_hash(md5, mv)
      return md5.digest()
docs: Obtains a signature for a `MetricValue`
  
      Args:
         mv (:class:`endpoints_management.gen.servicecontrol_v1_messages.MetricValue`): a
           MetricValue that's part of an operation
  
      Returns:
         string: a unique signature for that operation