Is stdin a tty? Use this to determine whether to provide prompt or just read stdin for input.

isatty.py

import sys

if sys.stdin.isatty():
    print('you are a tty')
else:
    print('you are not a tty')

output.md

$ python isatty.py 
you are a tty
$ echo foo | python isatty.py 
you are not a tty
$