“Input9)” is probably a typo for “input()”.

In Python 2, sys.stdin etc are by default wrappers around <stdio.h>’s “stdin” etc, and can easily be wrappers around other <stdio.h> FILE objects, so the PyOS_Readline API and Python’s “readline” module pass these <stdio.h> objects directly to rl_instream etc.

In Python 3, sys.stdin etc are not directly related to <stdio.h> objects. But the PyOS_Readline API was not changed, and the “readline” module still uses the rl_instream API which requires a <stdio.h> FILE object. So the new code decides if it is reasonable to substitute <stdio.h> “stdin” etc objects for the Python “sys” objects.