在 __add__ 运算符中返回相同子类的对象 [英] Returning object of same subclass in __add__ operator

问题描述

我正在为我自己的解释器开发一个简单的类型系统.我正在写这样的东西:

I am developing a simple type system for my own interpreter. I am writing something like this:

class Base(object):
    def __init__(self, content):
        self.__content = content

    @property
    def content(self):
        return self.__content

    @content.setter
    def content(self, value):
        self.__content = value

class Number(Base):
    def __init__(self, content):
        super(Number, self).__init__(content)

    def __add__(self, other):
        return Number(self.content + other.content)

    ...and so on

class Float(Number):
    def __init__(self, content):
        super(Float, self).__init__(content)

class Integer(Number):
    def __init__(self, content):
        super(Integer, self).__init__(content)

我的问题显然是如果我这样做:

My problem is that obviously if I do something like this:

if __name__ == '__main__':
    f1 = Float(3.5)
    f2 = Float(2.3)
    f3 = f1 + f2
    type(f3)

我对f1和f2求和了，它们是Float类型，但是我得到了f3，它是Number类型，但是我希望f3是Float类型.我怎么能在我的 Number 超类中定义一次添加运算符，返回与 f1 和 f2 相同的类型?我必须使用 isinstance 吗?有没有更干净的方法来做到这一点?

I have summed f1 and f2, which are Float type, but I have obtained f3, which is Number type, but I would like f3 to be a Float type. How could I define my add operator just one time in my Number superclass returning a type which is the same of f1 and f2? Have I to use isinstance? Is there a cleaner way to do this?

谢谢！

推荐答案

你可以用 __class__:

def __add__(self, other):
    return self.__class__(self.content + other.content)

正如@Eric 指出的那样，您可能想要做类似

As, @Eric points out, you may want to do something like

if self.__class__ == other.__class__:
    <use __class__>
else:
    <use Number>

确保可预测的行为(或在类不匹配时采取其他一些行动).

to ensure predicable behaviour (or some other action if the classes don't match).

__radd__ 也是值得在这里重写:

__radd__ is also worth overriding here:

__radd__ = __add__

这将使 Number(1) + Float(1) == Float(1) + Number(1) == Float(2)

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