#!/usr/bin/python3
 
l = [1, 2, 3, 4, 5, 6]
l.reverse()
for i in l:
  print(i)
   
# 出现问题，改变了原列表，不可取

#!/usr/bin/python3
 
l = [1, 2, 3, 4, 5, 6]
for i in l[::-1]:
  print(i)
   
# 得到了和原列表等大的列表，某种程度上很浪费

#!/usr/bin/python3
 
l = [1, 2, 3, 4, 5, 6]
 
for i in reversed(l):
  print(i)

#!/usr/bin/python3
 
 
class FloatRange(object):
  def __init__(self, start, end, step):
    self.dot = self.__get_dot_num(step)
    # 有多少个小数点就乘以10的多少次幂，因为浮点数运算不准确，换算成整形数进行计算
    self.start = start*pow(10, self.dot)
    self.end = end*pow(10, self.dot)
    self.step = step*pow(10, self.dot)
     
  def __get_dot_num(self, step):
    # 计算step有多少个小数点
    if isinstance(step, int):
      return step
    else:
      # 通过round实现计算有多少位小数，首创
      for dot in range(len(str(step))+1):
        if step == round(step, dot):
          return dot
 
  def __iter__(self):
    # 正向迭代
    while self.start <= self.end:
      yield self.start/pow(10, self.dot)
      self.start += self.step
 
  def __reversed__(self):
    # 反向迭代
    while self.end >= self.start:
      yield self.end/pow(10,self.dot)
      self.end -= self.step
 
if __name__ == '__main__':
   
  float_num_1 = FloatRange(2, 5, 0.1)
  float_num_2 = FloatRange(2, 5, 0.1)
   
  # 正向迭代
  for i in float_num_1:
    print(i)
     
  print('_'*60)
   
  # 反向迭代
  for x in reversed(float_num_2):
    print(x)