code: def mean(self, series, start, limit):
          '''
          :type start: int
          :type limit: int
          :rtype: float
          '''
          return float(np.mean(series[start:limit])f mean(self, series, start, limit):
          '''
          :type start: int
          :type limit: int
          :rtype: float
          '''
          return float(np.mean(series[start:limit]))
docs: :type start: int
          :type limit: int
          :rtype: float