Help understanding the decisions *behind* python? - immutable objects
nagle at animats.com
Mon Jul 27 03:06:36 EDT 2009
Steven D'Aprano wrote:
> On Sun, 26 Jul 2009 11:24:48 -0700, John Nagle wrote:
>> An interesting issue is Python objects, which are always mutable.
>> A "dict" of Python objects is allowed, but doesn't consider the contents
>> of the objects, just their identity (address). Only built-in types are
>> immutable; one cannot create a class of immutable objects.
> Yes you can, for some definition of "can":
> Admittedly pure Python objects are only "cooperatively immutable".
Right. I've been thinking about this as a way of improving
concurrency handling. The general idea is that objects shared
across threads would have to be either be immutable or synchronized.
Regular objects would be limited to a single thread. It's a path
to multithread programs without a global lock. Needs more work
to become a serious proposal. (It may not be worth the trouble;
a few years ago we were hearing about how 64-core CPUs were going
to become mainstream, but instead, the industry is going in the
direction of the same compute power for less money and with
less power consumption.)
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