If you are operating on a file that you opened in text mode, then you are correct that line breaks all show up as ‘\n‘. Otherwise, you are looking for os.linesep .
From http://docs.python.org/library/os.html:
os.linesep
The string used to separate (or, rather, terminate) lines on the
current platform. This may be a single
character, such as ‘\n’ for POSIX, or
multiple characters, for example,
‘\r\n’ for Windows. Do not use
os.linesep as a line terminator when
writing files opened in text mode (the
default); use a single ‘\n’ instead,
on all platforms.