> Is there an easy way for me to find the code for -u?

"-u" just passes 0 for the "buffering" argument to open() when creating
stdout and stderr. Otherwise "buffering" equals -1.
You can find equivalent code for open() in Lib/_pyio.py (the actual code
in is in C).

The practical difference is that "-u" removes the binary buffering layer
between the unicode layer and the raw file object:

$ ./python -c "import sys; print(sys.stdout, sys.stdout.buffer)"
<_io.TextIOWrapper name='<stdout>' encoding='UTF-8'> <_io.BufferedWriter name='<stdout>'>
$ ./python -u -c "import sys; print(sys.stdout, sys.stdout.buffer)"
<_io.TextIOWrapper name='<stdout>' encoding='UTF-8'> <_io.FileIO name='<stdout>' mode='wb'>

This should make absolutely no difference as to newline handling, since
that is handled exclusively in TextIOWrapper (binary layers are
transparent by construction).