TDLmake works now if I specify the path to tdlmake as part of the string passed to os.system. However, multiple command strings such as "cd "/Users/deastham/Desktop/RIBoutput"; /Applications/3Delight/bin/renderdl -D /Users/deastham/Desktop/RIBoutput/dgfg_0.rib" still don't work. (I am making sure to use the escape codes for slashes correctly. They are also used in the tdlmake calls.