'int isLoaded( string name )
Return the extruder that the given spool is loaded to. -1 if it is
not loaded for any extruder or None if the given name does not match
any known spool.'

def isLoaded(self, spool_name):

    spool_item = self._findByColumn(spool_name, 0)
    if (spool_item != (-1)):
        return spool_item[2]
    else:
        return None
