如何对浮点数和复数进行近似结构模式匹配

我读过并理解浮点数舍入问题 https://docs.python.org/3/tutorial/floatingpoint.html例如：

>>> sum([0.1] * 10) == 1.0
False

>>> 1.1 + 2.2 == 3.3
False

>>> sin(radians(45)) == sqrt(2) / 2
False

我也知道如何解决这些问题math.isclose() https://docs.python.org/3/library/math.html#math.isclose and cmath.isclose() https://docs.python.org/3/library/cmath.html#cmath.isclose.

问题是如何将这些解决方法应用于 Python match/case 语句。我希望这个工作：

match 1.1 + 2.2:
    case 3.3:
        print('hit!')  # currently, this doesn't match

解决方案的关键是构建一个重写的包装器__eq__方法并将其替换为近似匹配：

import cmath

class Approximately(complex):

    def __new__(cls, x, /, **kwargs):
        result = complex.__new__(cls, x)
        result.kwargs = kwargs
        return result

    def __eq__(self, other):
        try:
            return isclose(self, other, **self.kwargs)
        except TypeError:
            return NotImplemented

它为浮点值和复数值创建近似相等测试：

>>> Approximately(1.1 + 2.2) == 3.3
True
>>> Approximately(1.1 + 2.2, abs_tol=0.2) == 3.4
True
>>> Approximately(1.1j + 2.2j) == 0.0 + 3.3j
True

以下是如何在 match/case 语句中使用它：

for x in [sum([0.1] * 10), 1.1 + 2.2, sin(radians(45))]:
    match Approximately(x):
        case 1.0:
            print(x, 'sums to about 1.0')
        case 3.3:
            print(x, 'sums to about 3.3')
        case 0.7071067811865475:
            print(x, 'is close to sqrt(2) / 2')
        case _:
            print('Mismatch')

这输出：

0.9999999999999999 sums to about 1.0
3.3000000000000003 sums to about 3.3
0.7071067811865475 is close to sqrt(2) / 2