python中round(x、2)是什么意思,round方法python2.x与python3.x的差异

$ python

Python 2.7.8 (default, Jun 18 2015, 18:54:19)

[GCC 4.9.1] on linux2

Type "help", "copyright", "credits" or "license" for more information.

>>> round(0.5)

1.0

$ python3

Python 3.4.3 (default, Oct 14 2015, 20:28:29)

[GCC 4.8.4] on linux

Type "help", "copyright", "credits" or "license" for more information.

>>> round(0.5)

0

如果我们阅读一下python的文档，里面是这么写的：

在python2.7的doc中，round()的最后写着，"Values are rounded to the closest multiple of 10 to the power minus ndigits; if two multiples are equally close, rounding is done away from 0." 保留值将保留到离上一位更近的一端(四舍六入)，如果距离两端一样远，则保留到离0远的一边。所以round(0.5)会近似到1，而round(-0.5)会近似到-1。

但是到了python3.5的doc中，文档变成了"values are rounded to the closest multiple of 10 to the power minus ndigits; if two multiples are equally close, rounding is done toward the even choice." 如果距离两边一样远，会保留到偶数的一边。比如round(0.5)和round(-0.5)都会保留到0，而round(1.5)会保留到2。

所以如果有项目是从py2迁移到py3的，可要注意一下round的地方(当然，还要注意/和//，还有print，还有一些比较另类的库)。

>>> round(2.675, 2)

2.67