Are there any other better ways to access a single bit of string of digits?

[fl]

On Sunday, May 31, 2015 at 12:53:19 PM UTC-7, Denis McMahon wrote:
> On Sun, 31 May 2015 11:36:35 -0700, fl wrote:
> > I am new to Python. I would manipulate a string of hex numbers. If the
> > first digit is bigger than 7, the first two digits are required to add
> > 4.
> What happens if the first two digits are ff, does it become 103 or 03.
> If you have ffff_ffff_ffff
> Do you want to create 103ff_103ff_103ff
> or
> 03ff_03ff_03ff
> or
> newnums = [ bing(x) for x in oldnums ]
> 
> It could probably be done as a single list comprehension, but it might 
> get a bit messy.
> 
> -- 
> Denis McMahon, denismfmcmahon at gmail.com

Thanks for your reply. In fact, these data are from a 256 entries table. 
There is no extreme big data, such as Fxxxx.