CODEWITHSUNDEEP
python-3.xinputflush
Whack
Whack

Reputation: 153

Why does input flush stdout

When i create a subprocess and i communicate through stdin end stdout, then the messages dont arrive unless i either flush the buffer or execute input().

So i wonder if input() flushes the buffer, and if so i want to know why. 

# file1
import subprocess
import time
import select

process = subprocess.Popen(['python3',  'file2.py'], stdin=subprocess.PIPE, stdout=subprocess.PIPE)

read_ready, _, _ = select.select([process.stdout], [], [])
message = read_ready[0].readline().decode()
print(message)

time.sleep(11)

process.kill()

-

# file2
import sys
import time

print('1')

message = input()

# I added the sleep because the buffer gets flushed if the program stops
time.sleep(10)

If i execute this code it prints 1 immediatly. If i comment out the line with input(), then i need to wait until the file closes

Upvotes: 0

Views: 727

Answers (1)

Green Cloak Guy
Green Cloak Guy

Reputation: 24711

Yes, the input() function flushes the buffer. It has to, if you think about it - the purpose of the function is to present a prompt to the user and then ask for their input, and in order to make sure the user sees the prompt, the print buffer needs to be flushed.

Upvotes: 3

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