文本文件问题输出新文件

Python已知一文本文件中存放了若干逗号分隔的整数，将所有数降序排序后输出并写到一新文件中。大神们这怎么写代码啊，谢谢大佬

f = open("newFile.txt",'w')
with open("filename", 'r' ) as FA:
    for line in FA:
        line = line.strip().split(',')
        sortLine = line.sort(reverse = True)
        f.write(",".join(i for i in sortLine)+'\n')
f.close()