files creation question, any help plz ?

[wavic]

You are welcome! I did it so you can see that is not so complicated when you are doing it step by step. Tiny steps. As @Kebap said. 

Look at os.path module. os.path.join() takes a bunch of arguments and join them to create a properly formated path acording to the OS. 
os.path.join(dir, subdir, filename)

import os.path

dir_ = some_dir # dir is reserved word in Python. root is more suitable variable name :-)
subdir = subdir
file_name = '{}.txt'.format(element[0])
path = os.path.join(dir_, subdir, file_name)

with open(path, 'w') as out_file:
    # etc.

You can use os.path.abspath(dir) on dir to get the full path of the dir. As a precaution.