如何使用python将文件数据转换成二维列表

1,3,4
2,3,5
1,2,3,5
2,5

#!/usr/bin/env python
#coding=utf-8

def loadDataSet():    
    file = open("123.txt", "r")
    List_row = file.readlines()
 
    list_source = []
    for list_line in List_row:
        list_line = list(list_line.strip().split(','))
        
        s = []
        for i in list_line:
            s.append(int(i))
        
        list_source.append(s)
        
    return list_source

[[1,3,4],[2,3,5],[1,2,3,5],[2,5]]