Subprocess issue

test.py

import io,re,unittest,os,json,sys
from subprocess import PIPE, STDOUT, Popen
sub = Popen(["/usr/bin/python3.4", "test2.py", "pipe"], stdin=PIPE, stdout=PIPE, stderr=sys.stderr, close_fds=True, shell=False)
(writer,reader) = (sub.stdin, sub.stdout)
writer.write("HELO\t1\n".encode("utf-8"))
writer.flush()
sub.poll()
line = reader.readline().decode("utf-8")
assert(re.match("^OK\t", line))
writer.write("Q\ttest.com\tIN\tSOA\t-1\t127.0.0.1\n".encode("utf-8"))
line = reader.readline().decode("utf-8")
assert(re.match("^DATA\ttest.com\tIN\tSOA\t300\t-1\tsns.dns.icann.org. noc.dns.icann.org. 2013073082 7200 3600 1209600 3600", line))
sub.stdout.close()
sub.stdin.close()
sub.kill()
sub.wait()

test2.py

import sys
sys.stderr.write(sys.stdin.readline())
sys.stdout.write("OK\tversion foo bar hello\n")
sys.stdout.flush()
sys.stderr.write(sys.stdin.readline())
sys.stdout.write("DATA\ttest.com\tIN\tSOA\t300\t-1\tsns.dns.icann.org. noc.dns.icann.org. 2013073082 7200 3600 1209600 3600")
sys.stdout.flush()