错误：random的下标  第一个大于第二个
>>> random.randint(1,0)
 Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
   File "/home/nianxiongdi/anaconda3/lib/python3.6/random.py", line 221, in randint
     return self.randrange(a, b+1)
   File "/home/nianxiongdi/anaconda3/lib/python3.6/random.py", line 199, in randrange
     raise ValueError("empty range for randrange() (%d,%d, %d)" % (istart, istop, width))
ValueError: empty range for randrange() (1,1, 0)