alt Hacker NewsThis subject always seems to get bogged down in discussions about ordered vs. unordered keys, which to me seems totally irrelevant. No-one seems to mention the glaring shortcoming which is that, since dictionary keys are required to be hashable, Python has the bizarre situation where dicts cannot be dict keys, as in...
{{'foo': 'bar'}: 1, {3:4, 5:6}: 7}
...and there is no reasonable builtin way to get around this!
You may ask: "Why on earth would you ever want a dictionary with dictionaries for its keys?"
More generally, sometimes you have an array, and for whatever reason, it is convenient to use its members as keys. Sometimes, the array in question happens to be an array of dicts. Bang, suddenly it's impossible to use said array's elements as keys! I'm not sure what infuriates me more: said impossibility, or the python community's collective attitude that "that never happens or is needed, therefore no frozendict for you"
Turning a dictionary into a tuple of tuples `((k1, v1), (k2, v2), ...)`; isn't that a reasonable way?
If you want to have hash map keys, you need to think about how to hash them and how to compare for equality, it's just that. There will be complications to that such as floats, which have a tricky notion of equality, or in Python mutable collections which don't want to be hashable.