Python 3 detailed control of I/O of another process

Question

In python 3 (on Linux or MacOSX10.8) how can I get a parent process to read just a prompt (that does not include \n) issued by a subprocess, not the entire buffer till \n?

# program names.py
print("I am Joe.")                   #1print
name = input("What is your name? ")  #2prompt
print("Hi", name, "!")               #3print

# program parent.py (in python 3.3.0)
import subprocess
import sys
p = subprocess.Popen([sys.executable, "names.py"],
                      bufsize=0,
                      stdin =subprocess.PIPE,
                      stdout=subprocess.PIPE,
                      stderr=subprocess.PIPE,
                      shell=False,
                      universal_newlines=True
                    )
print(p.stdout.readline(), end='')
p.stdin.write("Sue\n")
# The next print will produce the output of 2prompt + 3print:
print(p.stdout.readline(), end='')

When I run parent.py it prints:

I am Joe.
What is your name? Hi Sue !

How to modify parent.py so that it prints:

I am Joe.
What is your name? 
Hi Sue !

That is, how to extract separately the output produced by prompt and print?

Answer 1

readline() reads from names.py until the next \n, where what you need is a "read as much as there is right now". Time is an additional factor here, since you basically have to detect, when names.py is waiting (expecting input).

Basically, you need a read()-operation with a timeout. You could start a separate thread that reads from names.py byte by byte into a buffer. You can then join(timeout) this thread and access its buffer.