redirect output of python script to file

Question

How do I get the output of this python script to append to a log file

sudo inotifywait -mr --format '%e%w%f' --event move $srdir | python3 /usr/bin/m-sync.py $bkdir $srdir >> /mnt/msync.py.log2 doesn't work. No error message, just an empty un-modified log file.

If I do just sudo inotifywait -mr --format '%e%w%f' --event move $srdir | python3 /usr/bin/m-sync.py $bkdir $srdir the output spits out to the console as expected.

Ultimately sudo inotifywait -mr --format '%e%w%f' --event move $srdir | python3 /usr/bin/m-sync.py $bkdir $srdir >> /mnt/msync.py.log2 is runs from a script as a service by systemd, but I don't think that's relevant since when I run it from the command line manually it still doesn't log.

In all cases the script actually does it's job correctly, I just can't get it's output into a log.

The python script just incase it matters:

#!/usr/bin/python3 import sys import time from subprocess import call src = "" bkdir = sys.argv[1] srdir = sys.argv[2] while True: line = sys.stdin.readline() event, path = line.split("/",1) path="/"+path.rstrip(); if event in ["MOVED_FROM","MOVED_FROM,ISDIR"]: src = path.replace(srdir, bkdir, 1) if event in ["MOVED_TO","MOVED_TO,ISDIR"]: dst = path.replace(srdir, bkdir, 1) sys.stdout.write(time.strftime("%Y-%m-%d %H:%M:%S") + " mv " + src + " " + dst ) call(["mv", src, dst]) 

Edit: Apparently sudo inotifywait -mr --format '%e%w%f' --event move $srdir | sudo python3 /usr/bin/m-sync.py $bkdir $srdir >> /mnt/msync.py.log2 run from the command line does work. Notice the second sudo before invoking python. However when run by systemd everything is root by default and still doesn't output to the log.

Answer 1

From https://stackoverflow.com/a/3167526/7192818

I don't know if this applies to python as well, but I think it depends on the operating system that you are running.

On Linux for example, output to terminal flushes the buffer on a newline, whereas for output to files it only flushes when the buffer is full (by default). This is because it is more efficient to flush the buffer fewer times, and the user is less likely to notice if the output is not flushed on a newline in a file.

You might be able to auto-flush the output if that is what you need.

So in the python script adding sys.stdout.flush() after the write makes it behave as expected.

Meh.