Chris Angelico <ros...@gmail.com>:
> On Thu, Nov 26, 2015 at 7:27 PM, Marko Rauhamaa <ma...@pacujo.net> wrote:
>> I have wanted to use lists as keys, and there should be no reason to
>> allow mutable tuples. It should be enough to say that the behavior of
>> a dictionary is undefined if a key should mutate on the fly.
>
> Python defines dict-key-validity as being synonymous with hashability.
> It's up to the class author to make sure the object's hash is useful.
>>> hash([])
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'list'
Annoying.
> Behaviour being undefined works just fine [1] in C. It's not so
> popular in Python. I don't think we want to have myriad new and
> experienced programmers trying to figure out why square brackets in
> dict keys are usually fine but occasionally not.
But there's no way to enforce that with any of the myriad new classes.
Ye blind guides, which strain at a gnat, and swallow a camel.
But I say unto you, Swallow the gnat as well.
Marko
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