How to specify Python version in script?

[kj]

I have a script that must be run with Python 2.6.x.  If one tries
to run it with, say, 2.5.x, *eventually* it runs into problems and
crashes.  (The failure is quicker if one attempts to run it with
Python 3.x.)

Is there some way to specify at the very beginning of the script
the acceptable range of Python versions?

TIA!

kynn

P.S. I know that I can hardcode the path to a specific intpreter
in the #! line, but I'm trying to keep the code a bit more general
than that.