Question

Is it possible to combine piped input and TTY prompts in Python CLI scripts? E.g., running this:

import sys

piped_text = None

if not sys.stdin.isatty():
    piped_text = sys.stdin.read()

user_in = raw_input('Enter something: ')

if piped_text:
    sys.stdout.write(piped_text)

sys.stdout.write(user_in + '\n')  

Produces the following output:

~: python mrprompt.py
Enter something: something
something
~: echo foo | python mrprompt.py
Enter something: Traceback (most recent call last):
  File "mrprompt.py", line 9, in <module>
    user_in = raw_input('Enter something: ')
EOFError: EOF when reading a line

When the output I’m looking for is this:

~: python mrprompt.py
Enter something: something
something
~: echo foo | python mrprompt.py
Enter something: something
foo
something

I guess, worded differently, is it possible for a subshell to know the tty of its parent shell? Is it possible, in Python, to interact a parent shell’s tty? I use bash inside of GNU Screen (therefore, reading the ‘SSH_TTY’ environment variable is not a viable option).

Answer 1

This works, more or less:

#!/usr/bin/python

import sys

saved_stdin = sys.stdin
sys.stdin = open('/dev/tty', 'r')
result = raw_input('Enter something: ')
sys.stdout.write('Got: ' + result + '\n')
sys.stdin = saved_stdin
result2 = sys.stdin.read()
sys.stdout.write('Also got: ' + result2)

Save as foo.py and try echo goodbye | ./foo.py

Of course, /dev/tty only exists on Unix. And if you run it in a process with no controlling terminal, the open() will probably fail…