python - 如何实现 __eq__ 进行集合包含测试？

Question

我遇到了一个问题，我将一个实例添加到一个集合中，然后进行测试以查看该对象是否存在于该集合中。我已经重写了 __eq__() 但在包含测试期间它没有被调用。我是否必须改写 __hash__()？如果是这样，我将如何实现 __hash__()，因为我需要散列元组、列表和字典？

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"

Answer 1

来自documentation on sets :

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__ function documentation建议将组件的哈希值异或在一起。正如其他人所提到的，散列可变对象通常不是一个好主意，但如果你真的需要，这行得通:

class DummyObj(object):

    ...

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

并检查它是否有效:

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

这打印:

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