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To: python-list@python.org
From: Christoph Groth <cwg@falma.de>
Subject: Re: dict: retrieve the original key by key
Date: Sun, 15 May 2011 12:46:15 +0200
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:5419

Steven D'Aprano <steve+comp.lang.python@pearwood.info> writes:

> On Sun, 15 May 2011 11:11:41 +0200, Christoph Groth wrote:
>
>> I would like to avoid having _multiple_ objects which are equal (a ==
>> b) but not the same (a is not b).  This would save a lot of memory.
>
> Based on the idea of interning, which is used for Python strings:
>
> cache = {} def my_intern(obj):
>     return cache.setdefault(obj, obj)
>
>
> x = make_some_object() x = my_intern(x)
>
> This ensures that equal objects in the graph are not just equal, but
> the same cached object.

This requires another dictionary, though.

But hey, they keys of my dictionary are actually strings, so I can use
the built-in intern.  Somehow, I have never stumbled accross this
built-in function so far.

Thanks a lot for the hint!

Christoph