I have two scripts. (Code is listed below). First script is just printing numbers with a delay.

Second script is supposed to start the first one as a subprocess, then checking in the background (!) if the first script outputting a number, and printing it if so.

But what I get is that the second script printing all of the numbers at once when first one is terminated (after 20 seconds) and not one number at each moment. Output is like:

START
0
1
2
3
4
5
6
7
8
9
16:05:51
OVER

But what I expect is something like:

START
0
16:05:51
1
16:05:53
2
16:05:55
3
16:05:57
4
16:05:59
5
16:06:01
6
16:06:03
7
16:06:05
8
16:06:07
9
16:06:09
OVER

How can I solve this?

Code:

1.py:

import time
for i in range(10):
    print(i)
    sys.stdout.flush()
    time.sleep(2)

test.py:

from subprocess import Popen, PIPE, STDOUT
from time import strftime
import threading, sys

stream = Popen(['python', '1.py'], stdout=PIPE, stderr=STDOUT)
def a():
        while True:
            try:
                out = stream.communicate()[0].decode("utf-8")
                print(out, strftime("%H:%M:%S"))
                sys.stdout.flush()
            except ValueError:
                print('OVER')
                break
            except:
                raise
t = threading.Thread(target=a,)
t.start()
print('START')