PEP 276 Simple Iterator for ints

[William Tanksley]

On Tue, 13 Nov 2001 13:31:21 -0800, James_Althoff at i2.com wrote:
>PEP: 276
>Title: Simple Iterator for ints

It's good to see someone doing useful work here.  PEPs are cool.

>Issues:
>    Based on some preliminary discussion on the Python interest
>    mailing list, the following concerns have been voiced:
>    - Is it obvious that iter(5) maps to the sequence 0,1,2,3,4?
>      Response: Given, as noted above, that Python has a strong
>      convention for indexing sequences starting at 0 and stopping at
>      (inclusively) the index whose value is one less than the length
>      of the sequence, it is argued that the proposed sequence is
>      reasonably intuitive to a Python programmer while being useful
>      and practical.

Strike the part about intuition.  Perhaps "consistent" would be strong
enough.

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
(immediately above).

>    - It would be better to reuse the ellipsis literal syntax (...)
>      Response: Shares disadvantages of other proposals that require
>      changes to the syntax.  Needs more design to determine how it
>      would handle the general case of start,stop,step,
>      open/closed/half-closed intervals, etc.  Needs a PEP.

The last sentance is the only one that matters here.  However, I'm
curious: what do you mean "reuse"?  I've never seen an "ellipsis literal"
in Python.  Reading through the Python documentation, I see an ellipsis
notation for extended slicing, but I'm in the dark as to what it means.
(I can guess, but I'd rather see it in print.)  I've never seen it in
Python code, and the documentation doesn't seem to mention it.

>    - 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.

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>.

>      Response: Same as previous response.  In addition, design
>      consideration needs to be given to what it would mean if one
>      uses slicing syntax after some arbitrary class other than class
>      int.  Needs a PEP.

Last sentance is still the most important one.  The second sentance is
nonsense; I don't have to define all possible class reactions to slicing
simply because I'm defining one!  This is equivalent to someone saying
that your PEP is bad because you don't define iter() for all classes.

I do, however, fail to define start, stop, and step behavior.  For this
reason I would propose that the PEP someone else writes for this suggest
'range' behavior, and require a start.

-- 
-William "Billy" Tanksley