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Re: iterating over list with one mising value

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  Re: iterating over list with one mising value Ian Kelly <ian.g.kelly@gmail.com> - 2012-02-07 09:03 -0700
    Re: iterating over list with one mising value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-02-08 01:50 +0000

#19965 — Re: iterating over list with one mising value

On Tue, Feb 7, 2012 at 5:27 AM, Sammy Danso <samdansobe@yahoo.com> wrote:
>
> Hello experts,
> I am having trouble accessing the content of my list.
> my list content has 2-pair value with the exception of one which has single value. here is an example  ['a', 1, 'b', 1, 'c', 3, 'd']
>
> I am unable to iterate through list to access invidual value pairs
>
> I get an error message saying ' the list should more than 1 value pairs'. I guess because 'd' has no value. How do I solve this problem?

What are you using to iterate through pairs instead of individual
elements?  It sounds like it is not very flexible.  I would recommend
instead using the "grouper" recipe from the itertools documentation:

http://docs.python.org/library/itertools.html#recipes

Cheers,
Ian

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#20001

(Apologies in advance for breaking threading, but the original post in 
this thread doesn't appear for me.)

> On Tue, Feb 7, 2012 at 5:27 AM, Sammy Danso <samdansobe@yahoo.com>
> wrote:
>>
>> Hello experts,
>> I am having trouble accessing the content of my list. my list content
>> has 2-pair value with the exception of one which has single value. here
>> is an example  ['a', 1, 'b', 1, 'c', 3, 'd']
>>
>> I am unable to iterate through list to access invidual value pairs


Here's a recipe to collate a sequence of interleaved items. It collects 
every nth item:


from itertools import islice, tee

def collate(iterable, n):
    t = tee(iter(iterable), n)
    slices = (islice(it, i, None, n) for (i, it) in enumerate(t))
    return [list(slice) for slice in slices]


And here it is in use:


>>> seq = [1, 'a', 'A', 2, 'b', 'B', 3, 'c', 'C', 4, 'd', 'D', 5, 'e']
>>> collate(seq, 3)
[[1, 2, 3, 4, 5], ['a', 'b', 'c', 'd', 'e'], ['A', 'B', 'C', 'D']]
>>> collate(seq, 2)
[[1, 'A', 'b', 3, 'C', 'd', 5], ['a', 2, 'B', 'c', 4, 'D', 'e']]
>>> collate(seq, 9)
[[1, 4], ['a', 'd'], ['A', 'D'], [2, 5], ['b', 'e'], ['B'], [3], ['c'], 
['C']]


-- 
Steven

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