Restricting the alphabet of a string

[John Machin]

On Apr 30, 9:53 pm, "Nathan Harmston" <ratchetg... at googlemail.com>
wrote:
> Hi,
>
> I ve being thinking about playing around with bit strings but use in
> some encoding problems I m considering and was trying to decide how to
> implement a bit string class. Is there a library out there for doing
> basic things with bit strings already is my first question?
>
> I know that I can extend string to bit string, but is there anyway I
> can force the alphabet to be restricted to 1's and 0's (or even 1, 0
> and -1, as an extension to from trinary strings).
>
> class Binary_String(String):
>     pass
>

See if you can pick which line below is impractically different to the
others:

binary: 0, 1
"trinary": -1, 0, 1
octal: 0, 1, 2, 3, 4, 5, 6, 7
decimal: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

HTH,
John