newbie string conversion question

[Scott David Daniels]

Rohit wrote:
> As part of a proprietary socket based protocol I have  to convert a
> string of length 10,
> 
> 	say, "1234567890"
> 
> to send it as 5 characters such that their hex values are
> 
> 	0x21 0x43 0x65 0x87 0x09
> 
> (Hex value of each character is got by transposing two digits at a
> time)
> 
>  How can I do this in python? I would like the result to be available
> as a string since I am concatenating it to another string before
> sending it out. 
> 
> Thanks,
> Rohit
> 
For a horrendously obscure version, try:

     def mangle(digits):
         length = (len(digits) + 1) >> 1
         v = int(digits, 16)
         mask = int('0F' * length, 16)
         smunch = (v ^ (v >> 4)) & mask
         swapped = v ^ (smunch | (smunch << 4))
         return ''.join(chr(255 & (swapped >> (8 * n)))
                        for n in reversed(range(length)))

--Scott David Daniels
scott.daniels at acm.org