Python相当于Java的compareTo() [英] Python equivalent of Java's compareTo()

问题描述

我正在用Python(3.2)做一个项目，为此我需要比较用户定义的对象.我习惯于用Java进行OOP，在Java中将在类中定义一个compareTo()方法，该方法指定该类的自然顺序，如下例所示:

I'm doing a project in Python (3.2) for which I need to compare user defined objects. I'm used to OOP in Java, where one would define a compareTo() method in the class that specifies the natural ordering of that class, as in the example below:

public class Foo {
    int a, b;

    public Foo(int aa, int bb) {
        a = aa;
        b = bb;
    }

    public int compareTo(Foo that) {
        // return a negative number if this < that
        // return 0 if this == that
        // return a positive number if this > that

        if (this.a == that.a) return this.b - that.b;
        else return this.a - that.a;
    }
}

我对Python中的类/对象还很陌生，所以我想知道定义类的自然排序的"pythonic"方法是什么?

I'm fairly new to classes/objects in Python, so I'd like to know what is the "pythonic" way to define the natural ordering of a class?

推荐答案

您可以实现特殊方法__lt__，__gt__等，以实现自定义类型的默认运算符.在语言参考中查看更多有关它们的信息.

You can implement the special methods __lt__, __gt__ etc. to implement the default operators for custom types. See more about them in the language reference.

例如:

class Foo:
    def __init__ (self, a, b):
        self.a = a
        self.b = b

    def __lt__ (self, other):
        if self.a == other.a:
            return self.b < other.b
        return self.a < other.b

    def __gt__ (self, other):
        return other.__lt__(self)

    def __eq__ (self, other):
        return self.a == other.b and self.b == other.b

    def __ne__ (self, other):
        return not self.__eq__(other)

或者如stranac在评论中所述，您可以使用 total_ordering 装饰器以保存一些输入内容:

Or as said by stranac in the comments, you can use the total_ordering decorator to save some typing:

@functools.total_ordering
class Foo:
    def __init__ (self, a, b):
        self.a = a
        self.b = b

    def __lt__ (self, other):
        if self.a == other.a:
            return self.b < other.b
        return self.a < other.b

    def __eq__ (self, other):
        return self.a == other.b and self.b == other.b

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