Python 3.7 math.remainder和％（模运算符）之间的区别 [英] Difference between Python 3.7 math.remainder and %(modulo operator)

问题描述

从 Python 3.7的新增功能
中，我们可以看到有一个新的 math.remainder 。它说

返回关于y的x的IEEE 754样式余数。对于有限x和有限非零y，这是差异 x-n * y ，其中n是最接近商精确值的整数x / y 。如果 x / y 恰好位于两个连续整数之间的中间位置，则对 n 使用最接近的偶数整数。余数 r =余数（x，y）因此始终满足 abs（r）< = 0.5 * abs（y）。

Return the IEEE 754-style remainder of x with respect to y. For finite x and finite nonzero y, this is the difference x - n*y, where n is the closest integer to the exact value of the quotient x / y. If x / y is exactly halfway between two consecutive integers, the nearest even integer is used for n. The remainder r = remainder(x, y) thus always satisfies abs(r) <= 0.5 * abs(y).

特殊情况遵循IEEE 754：特别地，对于任何有限x， remainder（x，math.inf）是x ，而 remainder（x，0）和 remainder（math.inf，x）提高任何非NaN x的ValueError 。如果其余操作的结果为零，则该零将具有与x相同的符号。

Special cases follow IEEE 754: in particular, remainder(x, math.inf) is x for any finite x, and remainder(x, 0) and remainder(math.inf, x) raise ValueError for any non-NaN x. If the result of the remainder operation is zero, that zero will have the same sign as x.

在使用IEEE 754二进制浮点的平台上，此操作的结果始终可精确表示：没有引入舍入错误。

On platforms using IEEE 754 binary floating-point, the result of this operation is always exactly representable: no rounding error is introduced.

但是我们还记得有 ％ 符号，

But we also remember that there is % symbol which is

x / y

的余数看到有一个给操作符的注释：

We also see that there is a note to operator:

不适用于复数。而是在合适的情况下使用 abs（）转换为浮点数。

我没有尝试运行

但是我尝试了

Python 3.6.1 (v3.6.1:69c0db5050, Mar 21 2017, 01:21:04)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import math
>>> 100 % math.inf
100.0
>>> math.inf % 100
nan
>>> 100 % 0
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ZeroDivisionError: integer division or modulo by zero

所以会有差异，而不是 nan 和 ZeroDivisionError ，我们将得到 ValueError ，如文档中所述。

So difference would be, instead of nan and ZeroDivisionError we would get ValueError as it says in docs.

所以问题是％和 math.remainder 有什么区别？ math.remainder 是否也可以用于复数（缺少它的％）？主要优点是什么？

So the question is what is the difference between % and math.remainder? Would math.remainder also work with complex numbers(% lacks from it)? What is the main advantage?

这是来自官方CPython github存储库中的 math.remainder 的来源。

推荐答案

返回关于y的x的IEEE 754样式余数。对于有限的
x和有限的非零y，这是差异 x-n * y ，其中n是最接近整数b的确切值的
。商 x / y 。如果 x / y 恰好是
在两个连续整数之间的中间位置，则n使用最接近的偶数
整数。余数 r =余数（x，y）因此始终
满足 abs（r）<= 0.5 * abs（y）。

Return the IEEE 754-style remainder of x with respect to y. For finite x and finite nonzero y, this is the difference x - n*y, where n is the closest integer to the exact value of the quotient x / y. If x / y is exactly halfway between two consecutive integers, the nearest even integer is used for n. The remainder r = remainder(x, y) thus always satisfies abs(r) <= 0.5 * abs(y).

对于模，这是 m = x-n * y ，其中 n 是 floor（x / y），因此 0 < = m< y 而不是 abs（r）< = 0.5 * abs（y）其余部分。

for the modulo this is m = x - n*y where n is the floor(x/y), so 0 <= m < y instead of abs(r) <= 0.5 * abs(y) for the remainder.

so

modulo(2.7, 1) = 0.7
remainder(2.7, 1) = -0.3

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