RSeQC sam2wig problem

[mdb@wistar]

I have recently tried all tools in the RSeQC pacakge; all work except bam2wig.py. It always gives error and quits:
"DeprecationWarning: the sets module is deprecated
import sets"

and it is not possble to modify the bam2wig.py downloaded from RseqC (by adding 'import sets' to the script) since it is read only. Any suggestions please, many thanks.