Scripts (running once)

[mixo]

How can one find out if there is a particular python script runnig, and
hence prevent
the same script from being run again? For instance, say I run a script
'mytes.py' with
the following command:

            python mytes.py

Now, the next time  a user types the same command, a message saying the
script is
already running (or something of that sort) should be printed, as the
script has not
termintated.