重写函数中的运算符

Question

我想为类函数中的类实例定义运算符，如下所示：

class MyClass(object):

    @property
    def _arithmetic_threshold(self):
        return self.threshold # this will be defined somewhere

    @_arithmetic_threshold.setter
    def _arithmetic_threshold(self,value):
        self.threshold = value
        self._define_arithmetic_attributes()

    def _define_arithmetic_attributes(self):
        """
        Wrapper to define all arithmetic attributes (in order to allow threshold changes)
        """

        self.__add__ = self._operation_wrapper(np.add,threshold=self._arithmetic_threshold)
        self.__sub__ = self._operation_wrapper(np.subtract,threshold=self._arithmetic_threshold)
        self.__mul__ = self._operation_wrapper(np.multiply,threshold=self._arithmetic_threshold)
        self.__div__ = self._operation_wrapper(np.divide,threshold=self._arithmetic_threshold)

然而，这似乎不起作用-我觉得我遗漏了一些关于操作符-、+等如何调用这些函数的信息。i、 电子邮件：

class MyClass2(object):
    def __add__(self,other,threshold=None):
        if threshold is not None:
            return self+other
        else:
            # do something here involving checking a threshold....
            pass

在MyClass2中，__add__的行为将不同。有谁能解释一下它们的不同之处，以及如何使MyClass中的操作符方法的行为类似于MyClass2？你知道吗

编辑：为了弄清楚我为什么要这么做，这里是_operation_wrapper。这个类是一个“光谱”对象，它有一个X轴和一个Y轴。目标是允许在Y轴上进行算术运算，但前提是X轴匹配。但是，它们可以匹配到1/5像素大小，所以我想做更多纯粹的“精确”匹配。你知道吗

def _operation_wrapper(operation):
    """
    Perform an operation (addition, subtraction, mutiplication, division, etc.)
    after checking for shape matching
    """

    def ofunc(self, other): 
        if np.isscalar(other):
            newspec = self.copy()
            newspec.data = operation(newspec.data, other) 
            return newspec
        else: # purely for readability

            if self._arithmetic_threshold == 'exact':
                xarrcheck = all(self.xarr == other.xarr)
            else:
                if self._arithmetic_threshold_units is None:
                    # not sure this should ever be allowed
                    xarrcheck = all((self.xarr-other.xarr) < self._arithmetic_threshold)
                else:
                    xarrcheck = all((self.xarr.as_unit(self._arithmetic_threshold_units)-other.xarr.as_unit(self._arithmetic_threshold_units)) < self._arithmetic_threshold)

            if self.shape == other.shape and xarrcheck:
                newspec = self.copy()
                newspec.data = operation(newspec.data, other.data)
                return newspec
            elif self.shape != other.shape:
                raise ValueError("Shape mismatch in data")
            elif not xarrcheck:
                raise ValueError("X-axes do not match.")

    return ofunc

Answer 1

像__add__()这样的特殊方法是在对象的类型上查找的，而不是在实例上。所以呢

a + b

大致翻译为

type(a).__add__(a, b)

这意味着在实例上设置__add__没有任何用处（除了使a.__add__(b)工作）。你知道吗

你的例子有点不完整，所以我不能提供完整的工作代码。您可以将代码从_define_arithmetic_attributes()移动到类主体，并从operation_wrapper()内部访问self.threshold。你知道吗

（注意，我没有理解_arithmetic_threshold属性的要点。为什么不直接访问self.threshold本身？）你知道吗