code: def add(self, iocb):
          
          if _debug: IOGroup._debug("add %r", iocb)
  
          # add this to our members
          self.ioMembers.append(iocb)
  
          # assume all of our members have not completed yet
          self.ioState = PENDING
          self.ioComplete.clear()
  
          # when this completes, call back to the group.  If this
          # has already completed, it will trigger
          iocb.add_callback(self.group_callback)
docs: Add an IOCB to the group, you can also add other groups.