[Python-Dev] Iterators (PEP 234)

[M.-A. Lemburg]

Christian Tismer wrote:
> 
> "M.-A. Lemburg" wrote:
> > > > Besides, the items() method has been around for ages, so switching
> > > > from .items() to .xitems() in programs will be just as easy as
> > > > switching from range() to xrange().
> > >
> > > It has been around for years, but key:value might be better.
> > > A little faster for sure since we don't build extra tuples.
> >
> > Small tuples are cheap and kept on the free list. I don't even
> > think that key:value can do without them.
> 
> a) I don't see a point to tell me about Python's implementation
> but for hair-splitting.

I'm not telling you (I know you know ;), but others on this list 
which may not be aware of this fact.

> Speed is not the point, it will just be
> faster. b) I think it can.
> But the point is the cleaner syntax which unambigously gets
> you keys and values, whenether the thing on the right can be indexed.
>
> > Anyway, I've already said that I'm -0 on these thingies -- I would
> > be +1 if Ping were to make key:value full flavoured associations
> > (Jim Fulton has written a lot about these some years ago; I think
> > they originated from SmallTalk).
> 
> I didn't read that yet. Would it contradict Ping's version or
> could it be extended laer?

Ping's version would hide this detail under the cover: 
dictionaries would sort of implement the sequence protocol
and then return associations. I don't think this is much
of a problem though.

> ...
> > > Having to force every "iterable" object to support a modified
> > > view of it via xitems() even doesn't look elegant to me.
> > > It forces key/value pairs to go through tupleization only
> > > for syntactical reasons. A weakness, not a strength.
> > > Object orientation gets at its limits here. If access to keys
> > > and values can be provided by a single implementation for
> > > all affected objects without adding new methods, this suggests
> > > to me that it is right to do so.
> >
> > Hey, tuples are created for *every* function call, even C calls
> > -- you can't be serious about getting much of a gain here ;-)
> 
> You are reducing my arguments to speed always, not me.
> I don't care about a tuple. But I think we can save
> code. Smaller *and* not slower is what I like.

At the cost of:

* special casing the for-loop implementation for sequences, mappings
* adding half a dozen new slots and methods
* moving all the complicated details into the for-loop implementation
  instead of keeping them in separate modules or object specific
  implementations

Perhaps we are just discussing the wrong things: I believe that
Ping's PEP could easily be implemented on top of my idea (or
vice-versa depending on how you look at it) of how the
iteration interface should look like.

-- 
Marc-Andre Lemburg
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