python3 subprocess stdin stdout communication

#!/usr/bin/python3
# parent.py
import sys
from subprocess import Popen, PIPE

with Popen([sys.executable, "child.py"], stdout=PIPE, stdin=PIPE, bufsize=1,
    universal_newlines=True) as p:
    for line in sys.stdin:
        line = line.rstrip('\n')
        print(line, file=p.stdin, flush=True)
        print(p.stdout.readline().rstrip('\n'), flush=True)


#!/usr/bin/python3
# child.py
import sys

for line in sys.stdin:
    line = line.rstrip('\n')
    print(line.upper(), flush=True)


#####
## multiple children example
#####

#!/usr/bin/python3
# parent.py
import sys
import time
from subprocess import Popen, PIPE

children = []

for i in range(5):
    p = Popen([sys.executable, "child.py", "%s" % i], stdout=PIPE, stdin=PIPE, bufsize=1,
        universal_newlines=True)
    children.append(p)

while children:
    for child in children:
        while child.poll() is None:
            line = child.stdout.readline().rstrip('\n')
            if line == "over" or not line:
                break
            print(line, flush=True)
        if child.poll() is not None:
            children.remove(child)

    time.sleep(0.1)



#!/usr/bin/python3
# child.py
import time
import sys

num = sys.argv[1]

for i in range(3):
    print("Children %s: %s" % (num, i), flush=True)
    print("over", flush=True)
    time.sleep(0.5)