code: def count(self, page_size=10, vtimeout=10, callback=None):
          
          def counted(a):
              if callable(callback):
                  callback(int(a['ApproximateNumberOfMessages']))
          self.get_attributes('ApproximateNumberOfMessages', callback=counted)
docs: Utility function to count the number of messages in a queue.
          Note: This function now calls GetQueueAttributes to obtain
          an 'approximate' count of the number of messages in a queue.