[Python-3000] Iterators for dict keys, values, and items == annoying :)

[Nick Coghlan]

Guido van Rossum wrote:
> On 3/23/06, Brett Cannon <brett at python.org> wrote:
>> But I think if objects returned iterators instead of lists the
>> iterator-as-view will begin to be used more than viewing them as
>> iterator-has-own-data.  But this also means that making a more
>> view-like interface would be handy.  In terms of what would need to be
>> supported (len, deletion, etc.) I don't know.  I personally have not
>> had that much of a need since I then just pass the originating object
>> and get the iterator as needed instead of passing around the iterator.
> 
> I'm dead set against giving iterators more view-like properties; it
> would rule out generators and other potentially infinite sequences.
> 
> But I'm all for a different concept, views in the sense of Java's
> collection framework. Please study it; it's worth it:
> 
> http://java.sun.com/j2se/1.4.2/docs/api/java/util/Collection.html

A very interesting read indeed (Their explanation in the Design FAQ regarding 
the use of 'UnsupportedOperationException' sounds downright Pythonic. . .)

Some more specific reading material can be found by looking at List.subList 
[1] along with Map.keySet, Map.entrySet and Map.values [2].

An interesting point is that making the views immutable doesn't really make 
life any easier, because you need to define what happens to the views if 
someone mutates the *original*. And once you do that, then that means you 
should be able to define what happens to the original if someone mutates the view.

I would be a big fan of adding views as a core concept - it would also provide 
a nice bridge to the way array slicing works in numpy (you get a mutable view 
rather than a copy).

Regards,
Nick.

[1]
http://java.sun.com/j2se/1.4.2/docs/api/java/util/List.html#subList(int,%20int)

[2]
http://java.sun.com/j2se/1.4.2/docs/api/java/util/Map.html#keySet()

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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