Python中"round"函数的行为

Question

任何人都可以解释我这段代码:

>>> round(0.45, 1)
0.5
>>> round(1.45, 1)
1.4
>>> round(2.45, 1)
2.5
>>> round(3.45, 1)
3.5
>>> round(4.45, 1)
4.5
>>> round(5.45, 1)
5.5
>>> round(6.45, 1)
6.5
>>> round(7.45, 1)
7.5
>>> round(8.45, 1)
8.4
>>> round(9.45, 1)
9.4

更新

我想这是因为浮动表示.我对吗？

Answer 1

你是对的.没有数字可以准确表示.在某些情况下,小数部分严格地大于0.45并且在某些情况下严格地小于:

In [4]: ['%.20f' % val for val in (0.45, 1.45, 2.45, 3.45, 4.45, 5.45, 6.45, 7.45, 8.45, 9.45)]
Out[4]: 
['0.45000000000000001110',
 '1.44999999999999995559',
 '2.45000000000000017764',
 '3.45000000000000017764',
 '4.45000000000000017764',
 '5.45000000000000017764',
 '6.45000000000000017764',
 '7.45000000000000017764',
 '8.44999999999999928946',
 '9.44999999999999928946']

这解释了看似不一致的舍入.