使用列表运算符"in"具有浮点值 [英] using list operator "in" with floating point values

问题描述

我有一个带有浮点数的列表，每个数字都有3个小数(例如474.259).如果我这样验证清单中的号码:

I have a list with floats, each number with 3 decimals (eg. 474.259). If I verify the number in the list like this:

if 474.259 in list_sample:
    print "something!"

然后显示该消息，但是如果我从另一个列表中取出该数字并四舍五入，则将其舍入:

Then the message is shown, but if I take the number from another list and I round it:

number = other_list[10]
number = round(number, 3)
if number == 474.259:
    print "the numbers are same!"
if number in list_sample:
    print "something!"

第二条消息未显示.

推荐答案

比较浮点数是否完全相等通常无法满足您的要求.这是因为计算机中的浮点数具有一种表示形式(存储格式)，这种表示形式对于许多实数本质上是不准确的.

Comparing floating point numbers for exact equality usually won't do what you want. This is because floating point numbers in computers have a representation (storage format) which is inherently inaccurate for many real numbers.

我建议在这里阅读: http://floating-point-gui.de/并使用ε"容差值进行模糊比较"之类的事情，以使数字相等，只要它们之间的差异小于x％或其他即可.

I suggest reading about it here: http://floating-point-gui.de/ and doing something like a "fuzzy compare" using an "epsilon" tolerance value to consider the numbers equal so long as they differ by less than x% or whatever.

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