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

You can do it by keeping track of where you are in the file and reopening it when you want to read. When the log file rotates, you notice that the file is smaller and since you reopen, you handle any unlinking too.

import time

cur = 0
while True:
    try:
        with open('myfile') as f:
            f.seek(0,2)
            if f.tell() < cur:
                f.seek(0,0)
            else:
                f.seek(cur,0)
            for line in f:
                print line.strip()
            cur = f.tell()
    except IOError, e:
        pass
    time.sleep(1)

This example hides errors like file not found because I'm not sure of logrotate details such as small periods of time where the file is not available.