了解集合的python对象成员资格

如果我理解正确，将调用对象的_cmp__;（）函数，以计算集合中的所有对象，同时确定对象是集合中的成员还是集合中的成员。 但是，对于集合而言，情况似乎并非如此：

class MyObject(object):
    def __init__(self, data):
        self.data = data

    def __cmp__(self, other):
        return self.data-other.data

a = MyObject(5)
b = MyObject(5)

print a in [b]          //evaluates to True, as I'd expect
print a in set([b])     //evaluates to False

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那么，如何在集合中测试对象成员身份？

集合在幕后使用dict，因此“in”语句检查对象是否作为dict中的键存在。由于对象未实现哈希函数，因此对象的默认哈希函数使用对象的id。因此，即使a和b是等效的，它们不是同一个对象，这就是正在测试的对象。

>xs=[]
>>> xs = []
>>> set([xs])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'list'

>>>集合（[xs]）
回溯（最近一次呼叫最后一次）：
文件“”，第1行，在
TypeError:不可损坏的类型：“列表”

给你。集合使用哈希，非常类似于dict。这对性能非常有帮助（成员资格测试是O（1），许多其他操作都依赖于成员资格测试），而且它也非常适合集合的语义：集合项必须是唯一的，不同的项将产生不同的哈希，而相同的哈希表示（理论上）重复

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由于默认的

\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu
 在类中添加
\uuuuuuuuuuuuuuuuuuuuuuuuuuuuu
方法会产生以下结果：

class MyObject(object):
    def __init__(self, data):
        self.data = data

    def __cmp__(self, other):
        return self.data - other.data

    def __hash__(self):
        return hash(self.data)


a = MyObject(5)
b = MyObject(5)

print a in [b] # True
print a in set([b]) # Also True!

正如其他人指出的，您的对象没有
\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu。谢谢：）//另外，感谢您发现我的非python本地评论习惯。