#!/usr/bin/python3 -BEOObbs
# coding=utf-8

import subprocess, sys

file = open('test.txt', 'bw')
file.write(b'1\n')
file.close()
pipe = subprocess.Popen(['diff', '-u', 'test.txt', '-'], stderr = subprocess.PIPE, stdin = subprocess.PIPE, stdout = subprocess.PIPE)
pipe.stdin.write(b'2\n')
pipe.stdin.flush()
#pipe.stdin.close()
print(pipe.stdout.read().decode())
pipe.wait()