License / Registration key enabled software

[T]

Mike Playle wrote:
> The people who want to use your software illegitimately will succeed no
> matter what you do, so you shouldn't worry about them. Worry instead about
> the people who DON'T want to use it illegitimately. Can a license key
> scheme help them? If so, implement it. No trickery is needed - a simple
> comparison will suffice.
>
> Mike

Oh man.  This is going way off topic!!!

I just wanted to know how license / registration key can be implemented
in python.  I was not interested in philosophical discussion of why /
why not one should implement it, whether that business model make
sense, instead using smartcards, etc. etc.

I would like to satisfy technical / intellectual curiosity of how it is
done in python -- so how about returning to the original topic of "How
can license / registration key be implemented in python?"