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Date: Fri, 01 Nov 2013 11:18:07 +0100
From: Ulrich Goebel <ml@fam-goebel.de>
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Subject: Re: "Backward"-Iterator - Beginners question
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Hi

Am 31.10.2013 23:35, schrieb Terry Reedy:
> On 10/31/2013 5:29 PM, Ulrich Goebel wrote:
>
>> I'm locking for an "iterator" type with not only the .next() method, but
>> with a .previous(), .first() and .last() method, so that I can through
>> it from the beginning or from the end, and in both directions, even
>> alternately (for example two steps forward, one backward, two steps
>> forward).
>
> You are free to write such a class, if it is appropriate for your actual
> use case.

Ok, possibly I will try that later...

> If you have a concrete sequence object seq with random access, there is
> no reason to do so. First and last are seq[0] and seq[-1]. Given
> 'cursor' i, prev and next are 'i-=1;seq[i]' and 'i+=1;seq[i]'.

That gives me the solution. What I have, is an iterator object comming 
as a SQLite database cursor object. So I could minimize the underliying 
SELECT and build index = list(cursor). Then with Your hints I get what I 
want.

Thanks
Ulrich

-- 
Ulrich Goebel
Paracelsusstr. 120, 53177 Bonn