code: def G_calc(item1, item2):
      
      try:
          result = math.sqrt(item1 * item2)
          return result
      except Exception:
          return "None"
docs: Calculate G-measure & G-mean.
  
      :param item1: PPV or TPR or TNR
      :type item1 : float
      :param item2: PPV or TPR or TNR
      :type item2 : float
      :return: G-measure or G-mean as float