[Tutor] using variables as args

[Alan Gauld]

> I'm trying to start a shell script with 4 arguments
> from my python script. I'm having problems trying to
> figure out the best way to do this. 

Use a format string:

cmd = "myscript %s %s %s %s"
os.system(cmd % (p1,p2,p3,p4))

OR

cmdstr = cmd % p1,p2,p3,p4
os.system(cmdstr)

The second form is easier to debug...

> to use popen3 to keep track of stdin, stdout, and err,

Ok, substitute popen3 for system().
Or better still use the subprocess module and 
the Popen class.

See the OS topic in my tutor for more on the subprocess 
module.

Alan Gauld
Author of the Learn to Program web site
http://www.freenetpages.co.uk/hp/alan.gauld