Re: (objects as) mutable dictionary keys
From: Antoon Pardon (apardon_at_forel.vub.ac.be)
Date: 01/17/05
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Date: 17 Jan 2005 08:34:59 GMT
Op 2005-01-14, Steve Holden schreef <steve@holdenweb.com>:
> Antoon Pardon wrote:
>
>> Op 2005-01-14, Peter Maas schreef <peter@somewhere.com>:
>>
>>>I have summarized the discussion about the usability of lists (and
>>>and other mutable types) as dictionary keys and put it into the
>>>Python wiki.URL: http://www.python.org/moin/DictionaryKeys.
>>>
>>>This summary might be used as a reference should the 'mutable
>>>dictionary keys' issue come up again in c.l.py.
>>>
>>
>> I had a look and I think you should correct the followingr:
>>
>> Dictionary lookup with mutable types like lists is a source of
>> unpleasant surprises for the programmer and therefore impossible in
>> Python.
>>
> Better, perhaps, to say:
>
> Dictionary lookup with mutable types like lists can be a
> source of unpleasant surprises for the programmer and
> therefore not recommended in Python.
IOW Python discourages mutable types in any type of container.
>> It is not impossible in Python. It may be discouraged but it is not
>> impossible since I have already done so.
>>
> If I discouraged you from shooting yourself in the foot would you do
> that too?
If I chose not to shoot my self in the foot, it wouldn't be because
you discouraged me. It would be because I heard good arguments.
What are good arguments or bad and how much weight they have depends
on the person and on the circumstances. So a simple rule like:
Never use a mutable as a key in a dictionary will sometimes not be
the best solution.
-- Antoon Pardon
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