如何实现__eq__进行集合包含测试？ [英] How to implement __eq__ for set inclusion test?

问题描述

我遇到了一个问题，即将实例添加到集合中，然后进行测试以查看该对象是否存在于集合中。我已覆盖 __ eq __（），但是在包含测试期间未调用它。我是否必须改写 __ hash __（）？如果是这样，鉴于我需要对元组，列表和字典进行哈希处理，我将如何实现 __ hash __（）？

I am running into an issue where I'm adding an instance to a set and then later testing to see whether or not that object exists in that set. I've overridden __eq__() but it doesn't get called during the inclusion test. Do I have to override __hash__() instead? If so, how would I implement __hash__() given that I need to hash the tuple, the list, and the dictionary?

class DummyObj(object):

    def __init__(self, myTuple, myList, myDictionary=None):
        self.myTuple = myTuple
        self.myList = myList
        self.myDictionary = myDictionary

    def __eq__(self, other):
        return self.myTuple == other.myTuple and \
            self.myList == other.myList and \
            self.myDictionary == other.myDictionary

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

if __name__ == '__main__':

    list1 = [1, 2, 3]
    t1    = (4, 5, 6)
    d1    = { 7 : True, 8 : True, 9 : True }
    p1 = DummyObj(t1, list1, d1)

    mySet = set()

    mySet.add(p1)

    if p1 in mySet:
        print "p1 in set"
    else:
        print "p1 not in set"

推荐答案

从关于文档的文档：

set类使用字典来实现。因此，set元素的
要求与字典
键的要求相同；也就是说，该元素同时定义了__eq __（）和__hash __（）。

The set classes are implemented using dictionaries. Accordingly, the requirements for set elements are the same as those for dictionary keys; namely, that the element defines both __eq__() and __hash__().

__ hash__函数文档建议将各组成部分的哈希值进行异或运算。正如其他人提到的那样，对可变对象进行散列通常不是一个好主意，但是，如果您确实需要，可以这样做：

The __hash__ function documentation suggests xor-ing the hashes of components together. As others have mentioned, it's generally not a good idea to hash mutable objects, but if you really need to, this works:

class DummyObj(object):

    ...

    def __hash__(self):
        return (hash(self.myTuple) ^
                hash(tuple(self.myList)) ^
                hash(tuple(self.myDictionary.items())))

并检查其是否有效：

p1 = DummyObj(t1, list1, d1)
p2 = DummyObj(t1, list1, d1)
mySet = set()
mySet.add(p1)

print "p1 in set", p1 in mySet
print "p2 in set", p2 in mySet

此打印：

$ python settest.py 
p1 in set True
p2 in set True

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