On Thu, 20 Apr 2006, Carroll, Barry wrote:

>  > The first step in the calculation is to split the input into two
>  strings:
>  > the even- and odd- numbered digits, respectively.  The least
>  significant
>  > digit is defined as odd.
>   
>  I forgot to include two important requirements:
>  
>      1. the length of the input string is arbitrary,
>      2. the order of the digits must be maintained.
>  
>  I could not find a way to include these requirements in a single, simple
>  expression.  

I really liked John Fouhy's approach, or at least a variation of it:

> >> def odd_even(s):
...    '''
...    Returns a tuple of two strings taken from s.  The first string is
...    the odd-numbered characters (counting from the right), and the
...    second is the even-numbered characters.
...    '''
...    return (s[::-2][::-1], s[-2::-2][::-1])
...
> >> odd_even("1234567")
('1357', '246')
> >> odd_even("2345")
('35', '24')
> >> odd_even("1")
('1', '')
> >>

John's original solution returned values with the digits in reverse 
order; but that's easily changed by reslicing each string with [::-1].

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