Tuples -- who needs 'em

Hrvoje Niksic hniksic at iskon.hr
Tue Apr 4 09:42:40 EDT 2000

Mike  Fletcher <mfletch at tpresence.com> writes:

> I think the point that is being made is this:
> 	The _value_ of a mutable object cannot (easily) be used as a
> dictionary key...
> 	i.e. in this sequence, what is the value of the final line...
> s = [ 1,2,3 ]
> p = { s: 4, [2,3,4]: 5 }
> s[:] = [2,3,4]
> p[ [2,3,4] ]

The second line raises a TypeError, therefore the last line does not
have a meaningful value.

I only noted that Fredrik's sentence, as it was formulated, was wrong.
Mutable collections can be used as dictionary keys, as long as they
provide a meaningful hash function.

More information about the Python-list mailing list