Python 没有内置的 frozendict 类型。事实证明这不会经常有用（尽管它可能仍然比frozenset现在更有用）。

需要这种类型的最常见原因是在记忆函数调用具有未知参数的函数时。存储 dict
的可散列等效项（其中值是可散列的）的最常见解决方案类似于tuple(sorted(kwargs.items())).

这取决于排序是否有点疯狂。Python 不能肯定地承诺排序会在这里产生一些合理的结果。（但它不能承诺太多其他东西，所以不要太多汗水。）

你可以很容易地制作某种类似于 dict 的包装器。它可能看起来像

import collections

class FrozenDict(collections.Mapping):
    """Don't forget the docstrings!!"""

    def __init__(self, *args, **kwargs):
        self._d = dict(*args, **kwargs)
        self._hash = None

    def __iter__(self):
        return iter(self._d)

    def __len__(self):
        return len(self._d)

    def __getitem__(self, key):
        return self._d[key]

    def __hash__(self):
        # It would have been simpler and maybe more obvious to 
        # use hash(tuple(sorted(self._d.iteritems()))) from this discussion
        # so far, but this solution is O(n). I don't know what kind of 
        # n we are going to run into, but sometimes it's hard to resist the 
        # urge to optimize when it will gain improved algorithmic performance.
        if self._hash is None:
            hash_ = 0
            for pair in self.items():
                hash_ ^= hash(pair)
            self._hash = hash_
        return self._hash

它应该很好用：

>>> x = FrozenDict(a=1, b=2)
>>> y = FrozenDict(a=1, b=2)
>>> x is y
False
>>> x == y
True
>>> x == {'a': 1, 'b': 2}
True
>>> d = {x: 'foo'}
>>> d[y]
'foo'