Python script not work in crontab

Question

Here is my script(randombg.py):

#!/usr/bin/env python 
# -*- coding: utf8 -*-

import random
import subprocess
import os 


BACKGROUND = '/home/david/wallpaper/dell2312'
IGNORE_FILES = ['/home/david/wallpaper/dell2312/.directory']


def enumerate():
    global BACKGROUND
    file_collections = []
    for root, dirs, files in os.walk(BACKGROUND):
        for file in files:
            file_collections.append(os.path.join(root, file))
    return file_collections


def randombg():
    select_files = list(set(enumerate())-set(IGNORE_FILES))
    subprocess.call(['feh', '--bg-scale', random.choice(select_files)])


def main():
    while 1:
        randombg()


if __name__ == '__main__':
    main()

I have run chmod a+x randombg.py and it worked with python randombg.py .Let's say its path is /path/to/randombg.py. Also, run /path/to/randombg.py worked.

However, when I added it to crontab as below:

1 * * * * /path/to/randombg.py 

or

01 * * * * python /path/to/randombg.py

or

01 * * * * /usr/bin/python /path/to/randombg.py

All failed.

I can't figure out. Could anyone explain?

PS: ArchLinux

---

More infomation

When I run ps aux|grep python , I can't find the randombg.py while sometimes it appears.

---

Addtional logs from crontab redirect stderr:

import: unable to open X server `' @   error/import.c/ImportImageCommand/361.
import: unable to open X server `' @ error/import.c/ImportImageCommand/361.
import: unable to open X server `' @ error/import.c/ImportImageCommand/361.
/home/david/dotfiles/randombg.py: line 9: BACKGROUND: command not found
/home/david/dotfiles/randombg.py: line 10: IGNORE_FILES: command not found
/home/david/dotfiles/randombg.py: line 13: syntax error near unexpected token `('
/home/david/dotfiles/randombg.py: line 13: `    def enumerate():'

Answer 1

Try to change your subprocess.call to

subprocess.call("export DISPLAY=:0; feh --bg-scale " + random.choice(select_files), shell=True)

This should export the DISPLAY variable, as scripts run from crontab do not have access to environmental variables by default.