Checking for duplicate instances of a script...

[Guillaume Dargaud]

Hello, python beginner here,
How can I make sure that a given script is never run more than once at the
same time in a system ?
Besides checking 'ps' for its own name. Most modern langages have a direct
way to do that.
Thanks
-- 
Guillaume Dargaud
http://www.gdargaud.net/
  "Here is your parachute and here is the manual.
  Welcome to Linux."