There is also the following consequence of (not) having the standard filenos: input() either considers the streams interactive or not. To consider them interactive, standard filenos and isatty are needed on sys.stdin and sys.stdout.

If the streams are considered interactive, input() goes via readlinehook machinery, otherwise it just writes and reads an ordinary file.

The latter means we don't have to touch readline machinery now, the downside is that custom rlcompleters like pyreadline won't work on input().