autofeh: auto wallpaper changer for i3wm

autofeh.py

#! /usr/bin/env python3

# change wallpaper every argv[2] seconds
# photo folder is argv[1]
# use "kill -s 10 `/tmp/autofeh.pid`" to change by yourself

import os
import sys
import time
import signal
import fcntl

print(os.getpid())

if len(sys.argv) >= 2:
    pic_folder = sys.argv[1]
else:
    pic_folder = "Photo/Wallpapers/"

if len(sys.argv) >= 3:
    interval = int(sys.argv[2])
else:
    interval = 20

cmd = "feh --bg-fill " + pic_folder + " --randomize"
master_changing = False
next_change_time = time.time()

def handler(*args):
    global next_change_time
    global master_changing

    if master_changing:
        return
    os.system(cmd)
    next_change_time = time.time() + interval

def file_lock():
    path = "/tmp/autofeh.pid"
    # open without rewrite
    f = open(path, 'a')
    try:
        fcntl.flock(f.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB)
    except BlockingIOError:
        return None

    # lock succeed, then rewrite
    f.truncate(0)
    f.write(str(os.getpid()))
    f.flush()
    return f

if __name__ == "__main__":
    lfile = file_lock()
    if lfile is None:
        raise Exception("another instance running")

    signal.signal(signal.SIGUSR1, handler)

    while True:
        if next_change_time <= time.time():
            # timeout
            master_changing = True
            os.system(cmd)
            next_change_time = time.time() + interval
            master_changing = False

        time.sleep(next_change_time - time.time())