When are immutable tuples *essential*? Why can't you just use lists *everywhere* instead?

[Neil Cerutti]

On 2007-04-21, Steven D'Aprano <steve at REMOVE.THIS.cybersource.com.au> wrote:
> On Fri, 20 Apr 2007 15:36:00 -0700, seberino at spawar.navy.mil wrote:
>>> The article explains that, amongst other things, tuples are
>>> faster than lists, so if you are working with constant values
>>> (inmutables) they are more indicated than lists.
>> 
>> Thanks.  I thought Python's design wasn't so concerned with
>> optimizations. Adding a new type "just" for optimization
>> reasons seems perhaps unnecessary.  I could be wrong.
>
> It's times like this I want to cry...
>
>
>>>> adict = {(1,2): "parrot"}
>
> Try replacing that tuple with a list. "Just optimization" my eye!

So the question becomes: Why do Python dictionaries require keys
to be of an immutable type?

-- 
Neil Cerutti