Re: Bug in string.find; was: Re: Proposed PEP: New style indexing,was Re: Bug in slice type

Antoon Pardon wrote:

Op 2005-08-31, Bengt Richter schreef <bokr@xxxxxx>:

On 31 Aug 2005 07:26:48 GMT, Antoon Pardon <apardon@xxxxxxxxxxxxxxx> wrote:


Op 2005-08-30, Bengt Richter schreef <bokr@xxxxxx>:

On 30 Aug 2005 10:07:06 GMT, Antoon Pardon <apardon@xxxxxxxxxxxxxxx> wrote:


Op 2005-08-30, Terry Reedy schreef <tjreedy@xxxxxxxx>:

"Paul Rubin" <"http://phr.cx"@NOSPAM.invalid> wrote in message news:7xy86k3r7n.fsf@xxxxxxxxxxxxxxxxxxxxxx


Really it's x[-1]'s behavior that should go, not find/rfind.

I complete disagree, x[-1] as an abbreviation of x[len(x)-1] is extremely useful, especially when 'x' is an expression instead of a name. 

I don't think the ability to easily index sequences from the right is
in dispute. Just the fact that negative numbers on their own provide
this functionality.

Because I sometimes find it usefull to have a sequence start and
end at arbitrary indexes, I have written a table class. So I
can have a table that is indexed from e.g. -4 to +6. So how am
I supposed to easily get at that last value?


Give it a handy property? E.g.,

table.as_python_list[-1] 

Your missing the point, I probably didn't make it clear.

It is not about the possibilty of doing such a thing. It is
about python providing a frame for such things that work
in general without the need of extra properties in 'special'
cases.


How about interpreting seq[i] as an abbreviation of seq[i%len(seq)] ?
That would give a consitent interpretation of seq[-1] and no errors
for any value ;-)



But the question was not about having a consistent interpretation for
-1, but about an easy way to get the last value.

But I like your idea. I just think there should be two differnt ways
to index. maybe use braces in one case.

  seq{i} would be pure indexing, that throws exceptions if you
  are out of bound

seq[i] would then be seq{i%len(seq)}

The problem with negative index's are that positive index's are zero based, but negative index's are 1 based. Which leads to a non symmetrical situations.

Note that you can insert an item before the first item using slices. But not after the last item without using len(list) or some value larger than len(list).

>>> a = list('abcde')
>>> a[len(a):len(a)] = ['end']
>>> a
['a', 'b', 'c', 'd', 'e', 'end']

>>> a[-1:-1] = ['last']
>>> a
['a', 'b', 'c', 'd', 'e', 'last', 'end']     # Second to last.

>>> a[100:100] = ['final']
>>> a
['a', 'b', 'c', 'd', 'e', 'last', 'end', 'final']


Cheers,
Ron














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