hashing mutable instances

[Michael Hudson]

Thomas Heller <theller at python.net> writes:

> Alex Martelli <aleax at aleax.it> writes:
> 
> [about object.__hash__]
> > Bernhard Herzog wrote:
> >    ...
> >> Good question. I didn't know that that was the default implementation of
> >> __hash__. It's not documented AFAICT, but it does seem to be the case. I
> >
> > I don't know why the official docs don't mention this fact -- I do
> > mention it in "Python in a Nutshell", of course (p. 132).
> >
> >> wonder why, even though it's useful.
> >
> > The reason this is done is because it's useful.
> 
> Well, Guido seems to disagree.  Per his request, when I complained about
> the default __hash__() method he asked me to enter a bug about it:
> http://www.python.org/sf/660098.  But it doesn't seem easy at all to fix
> this...

That's actually something different: new-style classes that define
__eq__ remain hashable.  I don't think making new-style classes that
*don't* define __eq__ *un*hashable is on the table, is it?  If it is,
let me complain about that :-)

Cheers,
mwh

-- 
  The proponent of the PEP shall be placed in a gladiatorial arena
  together with half a dozen hungry lions, and permitted to debate 
  the merits of the proposal with them.
                                       -- Greg Ewing, comp.lang.python