get each pair from a string.

[Emile van Sebille]

On 10/21/2012 11:51 AM, Ian Kelly wrote:
> On Sun, Oct 21, 2012 at 12:33 PM, Vincent Davis
> <vincent at vincentdavis.net> wrote:
>> I am looking for a good way to get every pair from a string. For example,
>> input:
>> x = 'apple'
>> output
>> 'ap'
>> 'pp'
>> 'pl'
>> 'le'
>>
>> I am not seeing a obvious way to do this without multiple for loops, but
>> maybe there is not :-)
>
> Use the "pairwaise" recipe from the itertools docs:
>
> def pairwise(iterable):
>      "s -> (s0,s1), (s1,s2), (s2, s3), ..."
>      a, b = tee(iterable)
>      next(b, None)
>      return izip(a, b)
>
>> In the end I am going to what to get triples, quads....... also.
>
> Generalizing:
>
> def nwise(iterable, n=2):
>      iters = tee(iterable, n)
>      for i, it in enumerate(iters):
>          for _ in range(i):
>              next(it, None)
>      return izip(*iters)
>



Hmmm.  And it seemed so straightforward to me as:

 >>> groupsize=3
 >>> a = "applesauce"
 >>> for i in range(len(a)-groupsize+1): a[i:i+groupsize]
...
'app'
'ppl'
'ple'
'les'
'esa'
'sau'
'auc'
'uce'

Other than adding depth to my knowledge of the ever growing standard 
library, is there a reason to prefer pairwise over my simple loop?

Emile