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[Python-ideas] Wild idea about mutability

Sven R. Kunze srkunze at mail.de
Mon Jun 6 03:05:40 EDT 2016 
On 02.06.2016 16:18, Joao S. O. Bueno wrote:
> Just remembering that one is free to implement whatever "switchable"
> containers one wants in the language as it is now - no need to force
> (full or slightly) incompatible  changes that imply on performance
> degradation onto every single Python user for a feature that was not
> needed up to this day.
>
> Implementing this in  sequence-abc, and mapping-abc classes is trivial.
>
> A reasonable request for the language could be exactly to allow a
> "__mutable__" property on the sequence, container and mapping
> protocols, and a "mutable" built-in callable, that in the absence of
> "__mutable__" could check for the methods signature (if it does not
> have "__mutable__" but has "__setitem__" , then mutable(obj) returns
> True, for example).

Is __setitem__ the only way to change an object?

> On 2 June 2016 at 10:55, Sven R. Kunze <srkunze at mail.de> wrote:
>> On 02.06.2016 15:05, Rob Cliffe wrote:
>>> Sure, there are many difficulties.
>>> This was intended to be a blue-sky idea.  I would like to pose the
>>> question "If I had to redesign Python from scratch, would I think this is a
>>> good idea?"
>>
>> I don't think that's an overly stupid idea. In such regard, Python wouldn't
>> be the first project dealing with mutability in this manner. PostgreSQL
>> already does.
>>
>> One question I would have: would it be enforced? Or can objects designer
>> choose between enforced immutability and informative immutability? Or would
>> it be enforced inconsistently at some places where at other places it does
>> not matter.
>> To me the 100% enforced variant would be the least troublesome.
>>
>> One definite advantage of broader use of immutable objects would be
>> optimization: using the same memory parts, re-using the same object etc.
>> It's not my field in computer science but other people will be able to
>> imagine a lot of other possibilities here.
>>
>> Best,
>> Sven
>>
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