We want to write bytes for convenience. This requires sys.stdout.buffer.
But using sys.stdout.buffer introducing buffered output. So we sprinkle
code with sys.stdout.flush() to force immediate writes.
After all that, Python 3 was emitting b'' prefixed output for errors.
So we only print errors if there were some. There aren't, so b'' don't
come into play and output is identical in Python 2 and 3.