Example usage of 'sh' library, illustrating ability to interact over stdin

sh_example.py

import os.path

import sh
from textwrap import dedent


this_line = []
nums = [4, 3, 2, 1]


def interact(char, stdin, process):
    print(char, end='', flush=True)
    if char == '\n':
        #print('line:', ''.join(this_line))
        this_line.clear()
        return
    this_line.append(char)
    if 'Square a number: ' in ''.join(this_line):
        try:
            n = nums.pop(0)
            #print('Putting', n)
            stdin.put(str(n) + '\n')
        except IndexError:
            print('<Killing>')
            process.signal(2)
            return True  # Stop calling this callback
        finally:
            this_line.clear()


pyfile = os.path.expanduser('~/tmp.py')

with open(pyfile, 'w') as f:
    f.write(dedent(
        """
        print("Starting")

        while True:
            n = input("Square a number: ")
            print(int(n)**2)
        """
    ))

p = sh.python(pyfile, _bg=True, _out=interact, _ok_code=1, _out_bufsize=0)
p.wait()