[Python-3000-checkins] r53724 - in python/branches/p3yk: Lib/test/test_dictviews.py Objects/dictobject.c

[Brett Cannon]

On 2/10/07, Guido van Rossum <guido at python.org> wrote:
> I meant the default implementation for 'in' which simply iterates over
> the collection. While 'in' can be implemented efficiently using the
> dict lookup for keys() and items(), for values() this doesn't work --
> if you want to know if a particular value is in dict.values(), you
> have to iterate over the entire dict until you find it.

Ah, OK.  So just 'in' get the iterator for the dict values view and
iterate through.  Makes sense now.

> (I had dreams
> of caching this by converting the values to a set, but was rudely
> awakened when I realized that values don't need to be hashable. So
> dict.values(), unlike dict.keys() and dict.items(), cannot return an
> object that behaves and is as efficient as a set, without copying
> anything; the only property I plan to implement (and have already done
> so) is __iter__ which gives all the values in random order.
>

Yeah, unless you want partial caching for those that are hashable, but
at that point it probably isn't worth it.

-Brett

> --Guido
>
> On 2/10/07, Brett Cannon <brett at python.org> wrote:
> > On 2/10/07, guido.van.rossum <python-3000-checkins at python.org> wrote:
> > > Author: guido.van.rossum
> > > Date: Sat Feb 10 19:55:06 2007
> > > New Revision: 53724
> > >
> > > Modified:
> > >    python/branches/p3yk/Lib/test/test_dictviews.py
> > >    python/branches/p3yk/Objects/dictobject.c
> > > Log:
> > > Implement __contains__ for dict_keys and dict_items.
> > > (Not for dict_values, where it can't be done faster than
> > > the default implementation which just iterates the elements.)
> >
> > What default implementation?  I assume you don't mean the default way
> > for dicts since you are already using that for keys and items.
> >
> > -Brett
> > _______________________________________________
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> > Python-3000-checkins at python.org
> > http://mail.python.org/mailman/listinfo/python-3000-checkins
> >
>
>
> --
> --Guido van Rossum (home page: http://www.python.org/~guido/)
>