比较浮点数和Python中几乎相等的最佳方法是什么？

朱雀 2023-03-05 04:28 43阅读 0赞

本文翻译自：[What is the best way to compare floats for almost-equality in Python?][What is the best way to compare floats for almost-equality in Python]

*It's well known that comparing floats for equality is a little fiddly due to rounding and precision issues.* **众所周知，由于舍入和精度问题，比较浮点数是否相等。**

*For example: [https://randomascii.wordpress.com/2012/02/25/comparing-floating-point-numbers-2012-edition/][https_randomascii.wordpress.com_2012_02_25_comparing-floating-point-numbers-2012-edition]* **例如： [https][https_randomascii.wordpress.com_2012_02_25_comparing-floating-point-numbers-2012-edition] ： [//randomascii.wordpress.com/2012/02/25/comparing-floating-point-numbers-2012-edition/][https_randomascii.wordpress.com_2012_02_25_comparing-floating-point-numbers-2012-edition]**

*What is the recommended way to deal with this in Python?* **在Python中处理此问题的推荐方法是什么？**

*Surely there is a standard library function for this somewhere?* **当然在某个地方有一个标准的库函数吗？**

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### \#1楼 ###

参考：[https://stackoom.com/question/ntCN/比较浮点数和Python中几乎相等的最佳方法是什么][https_stackoom.com_question_ntCN_Python]

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### \#2楼 ###

*I would agree that Gareth's answer is probably most appropriate as a lightweight function/solution.* **我同意Gareth的答案可能最适合作为轻量级功能/解决方案。**

*But I thought it would be helpful to note that if you are using NumPy or are considering it, there is a packaged function for this.* **但是我认为最好注意一下，如果您正在使用NumPy或正在考虑使用它，则可以使用打包功能。**

numpy.isclose(a, b, rtol=1e-05, atol=1e-08, equal_nan=False)

*A little disclaimer though: installing NumPy can be a non-trivial experience depending on your platform.* **不过有一点免责声明：根据您的平台，安装NumPy可能是不平凡的体验。**

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### \#3楼 ###

我发现以下比较有帮助：

str(f1) == str(f2)

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### \#4楼 ###

*For some of the cases where you can affect the source number representation, you can represent them as fractions instead of floats, using integer numerator and denominator.* **对于某些可能影响源编号表示的情况，可以使用整数分子和分母将它们表示为小数而不是浮点数。** *That way you can have exact comparisons.* **这样，您可以进行精确比较。**

*See [Fraction][] from fractions module for details.* **有关详细信息，请参见“ [分数][Fraction]的分数”模块。**

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### \#5楼 ###

*Python 3.5 adds the [`math.isclose` and `cmath.isclose` functions][math.isclose_ and _cmath.isclose_ functions] as described in [PEP 485][] .* **Python 3.5按照[PEP 485中的][PEP 485]描述添加了[`math.isclose`和`cmath.isclose`函数][math.isclose_ and _cmath.isclose_ functions] 。**

*If you're using an earlier version of Python, the equivalent function is given in the [documentation][] .* **如果您使用的是Python的早期版本，则等效功能在[文档中][documentation]给出。**

def isclose(a, b, rel_tol=1e-09, abs_tol=0.0):
        return abs(a-b) <= max(rel_tol * max(abs(a), abs(b)), abs_tol)

*`rel_tol` is a relative tolerance, it is multiplied by the greater of the magnitudes of the two arguments;* **`rel_tol`是一个相对公差，乘以两个自变量中的较大者；** *as the values get larger, so does the allowed difference between them while still considering them equal.* **当值变大时，它们之间的允许差异也会变大，同时仍将它们视为相等。**

*`abs_tol` is an absolute tolerance that is applied as-is in all cases.* **`abs_tol`是在所有情况下`abs_tol`应用的绝对公差。** *If the difference is less than either of those tolerances, the values are considered equal.* **如果差异小于这些公差中的任何一个，则认为值相等。**

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### \#6楼 ###

*If you want to use it in testing/TDD context, I'd say this is a standard way:* **如果要在测试/ TDD上下文中使用它，我会说这是一种标准方式：**

from nose.tools import assert_almost_equals
    
    assert_almost_equals(x, y, places=7) #default is 7

[What is the best way to compare floats for almost-equality in Python]: https://oldbug.net/q/ntCN/What-is-the-best-way-to-compare-floats-for-almost-equality-in-Python
[https_randomascii.wordpress.com_2012_02_25_comparing-floating-point-numbers-2012-edition]: https://randomascii.wordpress.com/2012/02/25/comparing-floating-point-numbers-2012-edition/
[https_stackoom.com_question_ntCN_Python]: https://stackoom.com/question/ntCN/%E6%AF%94%E8%BE%83%E6%B5%AE%E7%82%B9%E6%95%B0%E5%92%8CPython%E4%B8%AD%E5%87%A0%E4%B9%8E%E7%9B%B8%E7%AD%89%E7%9A%84%E6%9C%80%E4%BD%B3%E6%96%B9%E6%B3%95%E6%98%AF%E4%BB%80%E4%B9%88
[Fraction]: https://docs.python.org/2/library/fractions.html
[math.isclose_ and _cmath.isclose_ functions]: https://docs.python.org/3/whatsnew/3.5.html#pep-485-a-function-for-testing-approximate-equality
[PEP 485]: http://www.python.org/dev/peps/pep-0485
[documentation]: https://www.python.org/dev/peps/pep-0485/#proposed-implementation