Storing 'unhashable' types in dictionaries by address

[Ed Avis]

Chad Netzer <cnetzer at mail.arc.nasa.gov> writes:

>>>The builtin function id(x)

>>So now I can happily associate extra information with arbitrary
>>objects by using their address.
> 
>One thing to remember is that Python is free to reuse the object id (ie.
>address), after that object is deleted.

>Of course, it is likely the case when keeping track of ids, that you
>might also have a list of the objects, or some other way to keep
>track of them all (otherwise, what value is the id()?).

Indeed.  I wouldn't normally let go of an object but keep its entry in
a dictionary.  Still it's possible this gotcha could be a source of
subtle bugs.

The dictionary-wrapping class I suggested, which keeps track of the
object corresponding to each id and so allows objects to be used as
dictionary keys directly, would of course take care of this.

I didn't mention it at the time but I am thinking of something very
similar to Perl's Tie::RefHash module.

-- 
Ed Avis <ed at membled.com>