Way back when I started playing around with Python, one of the first applications I wrote was a transitioning background application. It worked quite nicely, but it was very tied to the Gnome 2 way of doing things and not particularly suited to a conversion to Gnome 3.
So now I have a simplified version which (after a bit of frustration) works quite nicely by simply displaying a random picture from my
~/Pictures/Backgrounds folder. The script, as it stands, looks like this:
""" Yet another, veryt simple background switcher for the Gnome 3 Desktop
Copyright (C) Paul Pritchard 2013
MTB3 is free software: you can redistribute it and/or modify it under the
terms of the GNU General Public License as published by the Free Software
Foundation, either version 3 of the License, or (at your option) any
MTB3 is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along
with this program. If not, see <http://www.gnu.org/licenses/>."""
backgrounds = os.environ['HOME'] + "/Pictures/Backgrounds/"
pictures = 
for filename in os.listdir(backgrounds):
mimetype = mimetypes.guess_type(filename)
if mimetype and mimetype.split('/') == "image":
picture = random.randrange (0, len(pictures))
fullpath = '"file:///' + backgrounds + pictures[picture] + '"'
os.system("DISPLAY=:0 GSETTINGS_BACKEND=dconf gsettings set org.gnome.desktop.background picture-uri '%s'" % (fullpath))
I then put a short script in
/usr/local/bin so that I could execute it with the
mtb command and, since everything was working swimmingly, I turned to cron to launch the app every 20 minutes.
The crontab line looks like this:
*/20 * * * * mtb
And it works, even if I have spent far too long finding my way around
There are a couple of points worth noting, if only for my own future sanity.
gsettings needs to know what screen to run on. This is fine when the command is executed from a terminal because it knows to run on the screen the terminal is sitting in. But when launching the same command from crontab, there is no terminal. You need, therefore, to include the
DISPLAY=:0 GSETTINGS_BACKEND=dconf to tell
gsettings where to run.
Secondly, the crontab environment settings are not always as complete as those found in Bash. So while I am able to enter just the command in Frugalware, other distributions may require you to use the full path to the command.