How to Stream Subprocess Output in Real-time using Python's `subprocess.communicate()`?

Streaming Output from subprocess.communicate()

In Python, using subprocess.communicate() to read stdout from a process that runs for an extended period can be problematic. The resulting output is received all at once, hindering real-time display.

To overcome this, it's possible to print each line of stdout as it's generated while still ensuring the process termination before proceeding:

Python 2

#!/usr/bin/env python2
from subprocess import Popen, PIPE

p = Popen(["cmd", "arg1"], stdout=PIPE, bufsize=1)
with p.stdout:
    for line in iter(p.stdout.readline, b''):
        print(line)
p.wait()  # Wait for subprocess termination

Python 3

#!/usr/bin/env python3
from subprocess import Popen, PIPE

with Popen(["cmd", "arg1"], stdout=PIPE, bufsize=1, universal_newlines=True) as p:
    for line in p.stdout:
        print(line, end='')

This modified approach continuously reads lines as they are written, bypassing the buffer delay. The process still retains its blocking behavior, halting execution until termination.

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