Python中除法使用的注意事项
本文实例讲解了Python中除法使用的注意事项，是非常重要的技巧，对于Python程序设计来说有很好的借鉴价值。具体分析如下：
现来看如下示例：
def avg(first, *rest): return (first + sum(rest)) / (1 + len(rest)) # Sample use avg(1, 2) # 1.5 avg(1, 2, 3, 4) # 2.5
源程序只是为了演示变长参数的使用，不过 Python 2.7.1 的解释器里，我得到的结果却和注释的结果不一样
>>> def avg(first, *rest): ... return (first + sum(rest)) / (1 + len(rest)) ... >>> avg(1, 2) 1 >>> avg(1, 2, 3, 4) 2
可以很明显的看到，小数点后的数据被截断了，我记得两个整数相除，"//" 应该才是取整，难道我记错了？
>>> def avg(first, *rest): ... return (first + sum(rest)) // (1 + len(rest)) # change '/' to '//' ... >>> avg(1, 2) 1 >>> avg(1, 2, 3, 4) 2
将 “/” 改成了“//”，得到的结果是一样的，“//”的确是取整这一点我是没记错，不过为什么“/”的结果也是截断了的？
同样的程序我在 3.4.1 的解释器里面做了测试，得到了预想的结果：
>>> def avg(first, *rest): ... return (first + sum(rest)) / (1 + len(rest)) ... >>> avg(1, 2) 1.5 >>> avg(1, 2, 3, 4) 2.5 >>> def avg(first, *rest): ... return (first + sum(rest)) // (1 + len(rest)) # change '/' to '//' ... >>> avg(1, 2) 1 >>> avg(1, 2, 3, 4) 2
可以看到在 3.4.1 的解释器里，“/”的结果保留了小数位，而“//”则是取整后的结果
搜索之后，找到了stackoverflow上的这个问题：Python里如何强制除法的结果为浮点数？ 注意这个是针对 2.x 的版本，3.x 里面并不存在这样的问题
答案的前两个解决方案，都很不错：
方法1：
>>> from __future__ import division >>> a = 4 >>> b = 6 >>> c = a / b >>> c 0.66666666666666663
方法2：
类似于C语言里面的做法：
c = a / float(b)
相信本文所述实例会对大家的Python程序设计有一定的帮助。
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