code: def get_stats_history(self, item=None, nb=0):
          
          s = self.get_json_history(nb=nb)
  
          if item is None:
              return self._json_dumps(s)
  
          if isinstance(s, dict):
              try:
                  return self._json_dumps({item: s[item]})
              except KeyError as e:
                  logger.error("Cannot get item history {} ({})".format(item, e))
                  return None
          elif isinstance(s, list):
              try:
                  # Source:
                  # http://stackoverflow.com/questions/4573875/python-get-index-of-dictionary-item-in-list
                  return self._json_dumps({item: map(itemgetter(item), s)})
              except (KeyError, ValueError) as e:
                  logger.error("Cannot get item history {} ({})".format(item, e))
                  return None
          else:
              return None
docs: Return the stats history (JSON format).