How to Tail Log Files in Python Without Blocking?

Tailing Log Files in Python

Q: Is there a non-blocking or locking way to tail a log file in Python, similar to the command tail -F? While there's an older method, is there a better solution or library available?

A: Non-Blocking:

On Linux, utilizing the subprocess and select modules offers a non-blocking solution:

import time
import subprocess
import select

f = subprocess.Popen(['tail','-F',filename],\
        stdout=subprocess.PIPE,stderr=subprocess.PIPE)
p = select.poll()
p.register(f.stdout)

while True:
    if p.poll(1):
        print f.stdout.readline()
    time.sleep(1)

This solution polls the output pipe for new data and displays it immediately. You can replace time.sleep(1) and print f.stdout.readline() with custom functionalities.

Blocking:

For a blocking approach, you can use the subprocess module without additional modules:

import subprocess
f = subprocess.Popen(['tail','-F',filename],\
        stdout=subprocess.PIPE,stderr=subprocess.PIPE)
while True:
    line = f.stdout.readline()
    print line

This method will also print new lines as they emerge, but it will halt execution until the tail process is terminated (e.g., via f.kill()).

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