PEP 276 Simple Iterator for ints
wtanksle at dolphin.openprojects.net
Wed Nov 14 22:34:34 CET 2001
On Tue, 13 Nov 2001 17:00:29 -0800, James_Althoff at i2.com wrote:
>William Tanksley wrote:
>>On Tue, 13 Nov 2001 13:31:21 -0800, James_Althoff at i2.com wrote:
>>I'm not sure I like this aspect anyhow. "5" just doesn't seem similar to
>>"0,1,2,3,4". A single integer isn't a range.
>>> - Possible ambiguity
>>> for i in 10: print i
>>> might be mistaken for
>>> for i in (10,): print i
>>> Response: The predicted ambiguity was not readily apparent to
>>> several of the posters.
>>You'll have to do better than that. This is the same problem as issue 1
An important point. "for i in 10,:" is an enormously different thing
under this proposal that "for i in 10:"
>>> - It would be better to reuse the slicing literal syntax attached
>>> to the int class, e.g., int[0:10]
>>No. I said that would be better to implement __getslice__ as a
>>sequence-returning class method of the int class, e.g. int[0:10]. I'm not
>>interested in proposing syntax changes.
>Got it. But can __getslice__ be changed from an instance method to a class
>method for types.IntType and still work without special casing? I don't
>know about this.
Chris posted a quick and dirty hack which works, or appears to work. At
any rate, it demonstrates the concept.
>In any case, presumably the returned sequence would be auto-converted to a
>lightweight iterator in the for-loop (as lists are). Seems that PEP 276
>has the advantage of directly creating an iterator without the need of
>first creating a sequence object.
My intention was to have this __getslice__ return a generator, not a
tuple. It's clear that I'm proposing occasionally infinite slices, so
generating a sequence would be phenominally foolish :-). I would also
like to have the returned object implement __getitem__, since it's
relatively easy, but that's a different topic.
>>I claim that it's better because your method because your method doesn't
>>_look_ like a range and doesn't act like other Python usages. In essence,
>>it makes Python integers behave differently in scalar context versus array
>>context -- and we can't have people comparing us to that OTHER P***
>>language <0.4 wink>.
Python already has one expression which behaves differently in a loop
>However, I'm still unclear on the notion of __getslice__ being sometimes
>an instance method and sometimes a class method. The code generated from
>the slicing syntax would have to try to call it both ways or something, I
I don't see why -- you just call the __getslice__ method of the object
you're thrown at. Aren't builtin types also objects?
>Agree with you that a PEP would be good. ;-)
Here's a place I wish people would stop agreeing with me. :-)
-William "Billy" Tanksley
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