code: def percentile(sorted_list, percent, key=lambda x: x):
      if not sorted_list:
          return None
      if percent == 1:
          return float(sorted_list[-1])
      if percent == 0:
          return float(sorted_list[0])
      n = len(sorted_list)
      i = percent * n
      if ceil(i) == i:
          i = int(i)
          return (sorted_list[i-1] + sorted_list[i]) / 2
      return float(sorted_list[ceil(i)-1])