python中的负零

问题描述

我在 python 的输出中遇到负零；例如，它的创建如下:

I encountered negative zero in output from python; it's created for example as follows:

k = 0.0
print(-k)

输出将是 -0.0.

但是，当我将 -k 与 0.0 进行比较时，结果为 True.0.0 和 -0.0 之间有什么区别吗(我不在乎它们可能具有不同的内部表示；我只关心它们在程序中的行为.)有什么我应该注意的隐藏陷阱吗?

However, when I compare the -k to 0.0 for equality, it yields True. Is there any difference between 0.0 and -0.0 (I don't care that they presumably have different internal representation; I only care about their behavior in a program.) Is there any hidden traps I should be aware of?

推荐答案

查看 -0(维基百科中的数字)

基本上 IEEE 确实定义了一个负零.

Basically IEEE does actually define a negative zero.

并且根据这个定义用于所有目的:

And by this definition for all purposes:

-0.0 == +0.0 == 0

我同意 aaronasterling -0.0 和 +0.0 是不同的对象.使它们相等(相等运算符)可确保代码中不会引入细微的错误.
想想 a * b == c * d

I agree with aaronasterling that -0.0 and +0.0 are different objects. Making them equal (equality operator) makes sure that subtle bugs are not introduced in the code.
Think of a * b == c * d

>>> a = 3.4
>>> b =4.4
>>> c = -0.0
>>> d = +0.0
>>> a*c
-0.0
>>> b*d
0.0
>>> a*c == b*d
True
>>> 

当我出于所有实际目的说这个词时，我是相当仓促地选择了这个词.我的意思是标准的平等比较.

When I said for all practical purposes, I had chosen the word rather hastily. I meant standard equality comparison.

正如参考资料所说，IEEE 标准定义了比较，以便 +0 = -0，而不是 -0 .+0.尽管总是可以忽略零的符号，但 IEEE 标准并没有这样做.当乘法或除法涉及带符号的零时，通常的符号规则适用于计算答案的符号.

>>> divmod(-0.0,100)
(-0.0, 0.0)
>>> divmod(+0.0,100)
(0.0, 0.0)

>>> math.atan2(0.0, 0.0) == math.atan2(-0.0, 0.0)
True 
>>> math.atan2(0.0, -0.0) == math.atan2(-0.0, -0.0)
False