python: read file continuously, even after it has been logrotated

Question

I have a simple python script, where I read logfile continuosly (same as tail -f)

while True:
    line = f.readline()
    if line:
        print lin         


        

Answer 1

As long as you only plan to do this on Unix, the most robust way is probably to check so that the open file still refers to the same i-node as the name, and reopen it when that is no longer the case. You can get the i-number of the file from os.stat and os.fstat, in the st_ino field.

It could look like this:

import os, sys, time

name = "logfile"
current = open(name, "r")
curino = os.fstat(current.fileno()).st_ino
while True:
    while True:
        buf = current.read(1024)
        if buf == "":
            break
        sys.stdout.write(buf)
    try:
        if os.stat(name).st_ino != curino:
            new = open(name, "r")
            current.close()
            current = new
            curino = os.fstat(current.fileno()).st_ino
            continue
    except IOError:
        pass
    time.sleep(1)

I doubt this works on Windows, but since you're speaking in terms of tail, I'm guessing that's not a problem. :)