Why are tuples immutable?
Antoon Pardon
apardon at forel.vub.ac.be
Thu Dec 16 03:44:49 EST 2004
Op 2004-12-15, Steve Holden schreef <steve at holdenweb.com>:
> Antoon Pardon wrote:
>
>> Op 2004-12-15, Roel Schroeven schreef <rschroev_nospam_ml at fastmail.fm>:
>>
>>>Antoon Pardon wrote:
>>>
>>>>Op 2004-12-15, Fredrik Lundh schreef <fredrik at pythonware.com>:
>>>>
>>>>>sorry, but I don't understand your reply at all. are you saying that dictionaries
>>>>>could support mutable keys (e.g lists) by making a copy of the key? how would
>>>>>such a dictionary pick up changes to the original key object? (I'm talking about
>>>>>the key stored in the dictionary, not the key you're using to look things up).
>>>>
>>>>
>>>>You want to mutate a key that is within a dictionary?
>>>
>>>No, we don't want to mutate it; as far as I know, that is exactly the
>>>reason why dictionaries don't support mutable keys.
>>
>>
>> And I think that is a stupid reason. There are enough other situations
>> were people work with mutable objects but don't wish to mutate specific
>> objects. Like objects in a sorted sequence you want to keep that way
>> or objects in a heapqueue etc.
>>
>> Demanding that users of dictioanaries somehow turn their mutable objects
>> into tuples when used as a key and back again when you retrieve the keys
>> and need the object can IMO ibe a bigger support nightmare than the
>> possibility that code mutates a key in a dictionary.
>>
> So provide your objects with a __hash__ method, and you can use them as
> dictionary keys.
>
> Sheesh, learn Python already. What a troll. [Plonk]
>
Let me get this straight.
You first say dictionaries don't support mutable keys for some reason.
I say I find it a stupid reason.
Then you mark me a troll because I don't know the language while at
the same time making a suggestion that implies your original remark
about python was wrong.
--
Antoon Pardon
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