strings for beginers

[Sapote]

I am attempting to modify a python program (Discspan) that I
downloaded from sourceforge.  I know nothing of Python and little of
programming.

The program will back ups large numbers of files to  to multiple
DVDs.  The burning routine was rather primitive I have modified the
burn burn_cmd to write an iso file to the hard drive.  Unnfortunately
I do not understand the string building that is going on here

I have an incrementing variable disc_num that I could insert in the
line below to create discspanisoX.iso where X is incrementing...

  burn_cmd = "mkisofs   -udf  -o /home/donkey/discspaniso.iso -graft-
points --path-list %s" %(temp_list)
 
^^^^^