三层文件夹的文件遍历

import os
fin = 'D:\data_sex\'
fout = 'D:\data_sex\'
print(os.listdir(fin))
for file in os.listdir(fin):
    file_fullname = fin + '\' +file
    print(file_fullname)
    for file2 in os.listdir(file_fullname):
        file_fullname2 = file_fullname + '\' + file2
        print(file_fullname2)
        for file3 in os.listdir(file_fullname2):
            file_fullname3 = file_fullname2 + '\' + file3
            print(file_fullname3)