> On Windows, stdin, stdout and stderr are creates using TextIOWrapper(..., newline=None).
> In this case, TextIOWrapper._writenl is os.linesep and so '\r\n'.

Oh, I was wrong: stdin is created with newline=None, but stdout and stderr are created with newline="\n" and so "\n" is not translated to "\r\n".

I checked in Python 2.7: print("abc") and sys.stdout.write("abc\n") writes b"abc\r\n" into the output file (when the output is redirected), but sys.stdout.write("abc\r\n") writes b"abc\r\r\n". Python 3.3 should do the same: \r\n is preferred on Windows (ex: notepad doesn't support UNIX line ending, \n).

Attached patch changes line ending for stdout and stderr on Windows: translate "\n" to "\r\n".

It would be nice to fix this before Python 3.3 final.