python中的取整

处理数据时，经常会遇到取整的问题，现总结如下

1，向下取整 int()

 >>>a = 3.1
 >>>b = 3.7
 >>>int(a)
  3
 >>>int(b)
  3
 >>>int(-a)
  -3
 >>>int(-b)
  -3

2，向上取整 math.ceil()

 >>>from math import ceil
 >>>a = 3.1
 >>>b = 3.7
 >>>ceil(a)
 4
 >>>ceil(b)
 4
 >>>ceil(-a)
 -3
 >>>ceil(-b)
 -3

3，四舍五入 round()

 >>>a = 3.123
 >>>b = 3.256
 >>>round(a)
 3.0
 >>>round(a, 2)
 3.12
 >>>round(b, 2)
 3.26
 >>>round(b, 1)
 3.3