How Can I Simultaneously Capture and Display Live Output from a Subprocess in Python?

Print Live Output While Storing Subprocess Command Output

When invoking a subprocess using subprocess.Popen, we can simultaneously store its output for logging purposes and display it live on the terminal.

Possible Solutions

Option 1: Using Iterators

import subprocess
import sys

with open("test.log", "wb") as f:
    process = subprocess.Popen(your_command, stdout=subprocess.PIPE)
    for c in iter(lambda: process.stdout.read(1), b""):
        sys.stdout.buffer.write(c)
        f.buffer.write(c)

Option 2: Using a Reader and a Writer

import io
import time
import subprocess
import sys

filename = "test.log"
with io.open(filename, "wb") as writer, io.open(filename, "rb", 1) as reader:
    process = subprocess.Popen(command, stdout=writer)
    while process.poll() is None:
        sys.stdout.write(reader.read())
        time.sleep(0.5)
    # Read the remaining
    sys.stdout.write(reader.read())

Option 3: Custom Solution

ret_val = subprocess.Popen(run_command,
                            stdout=log_file,
                            stderr=subprocess.PIPE,
                            shell=True)
while not ret_val.poll():
    log_file.flush()

In another terminal, run:

tail -f log.txt

With these methods, you can capture subprocess output while also displaying it live, ensuring both logging and progress monitoring.

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