自定义了一个函数如下：

def loopTables(dt, tm ,seqno, dfspath, tablename ,mutable tmCol ,mutable seqCol ){ 
	if(NULL == tmCol) tmCol = "tserial"
	if(NULL == seqCol) seqCol = "seqno"


	print("delete specific rows done!")
	
	dbs = "dfs:/"+getAllDBs().keys()
	for(dbpath in dbs){
		print(dbpath)
		tbls = getTables(database(dbpath))
		print(tbls)
		for(tablename in tbls){
			print(tablename)
			colNames = loadTable(dbpath, tablename).schema().colDefs.name
			if(in(tmCol, colNames) && in(seqCol, colNames)){
				print(dbpath + ":" + tablename + " begin delete ")
			}else{
				print("no need for delete " + dbpath + ":" + tablename)
			}
		}
	}
}

想法是，先遍历库，再遍历表，但是调用函数后报错：tbls => Can't assign an object to an existing constant variable.

但是把代码拉出来执行却没有问题，这是为什么？