I think the correct way to do the in-kernel query using a string argument in your case would be:
conditon="(IndexColumn==1)|(IndexColumn==6)|(IndexColumn==7)|(IndexColumn==9)"
and IndexColumn needs to be the actual name of the column as specfied in your IsDescription class. I believe the python condition "a in b" is not valid for Pytablles queries
EDIT concerning your comment:
"".join(["(IndexColumn==%i)|"%j for j in selectedIndex])[:-1]
should give you the correct string for the query.