The os.write function can be used to writes bytes into a file descriptor (not file object). If I execute os.write(fd, '\n'), only the LF character will be written into the file, even on Windows. I would like to have CRLF in the file on Windows and only LF in Linux.
What is the best way to achieve this?

I'm using Python 2.6, but I'm also wondering if Python 3 has a different solution.

Use this

import os
os.write(fd, os.linesep)