Wallpaper Changer

#!/usr/bin/env python
#
# bg_slideshow.py
# (c) 2012 MB http://somethingididnotknow.wordpress.com
#
# This script is released under WTFPL, but it's heavily inspired from Romano
# Giannetti's original bg_slideshow.py
# See http://rlog.rgtti.com/software/linux/wallpaper-slideshow-for-gnome3/
#
# A simple wallpaper changer for GNOME desktop.
# List your wallpapers folders in file ~/.bg_slideshow.conf and run the script:
#
# python bg_slideshow.py &
#
# or add a startup entry using gnome-session-properties
import sys
import os
import random
from time import gmtime, sleep, strftime

class WallpaperChanger:
    # conf file is in ~/.bg_slideshow.conf change it here if you want
    conf_file = os.path.join(os.getenv("HOME"), '.bg_slideshow.conf')
    mode = "zoom" # one of none, centered, wallpaper, scaled, stretched, zoom, spanned
    delay = 3 * 60 # in seconds
    formats = [".jpg", ".png", ".gif", ".jpeg"] # accepted formats
    files = []
    all_files = set()

    def __init__(self):
        self.index = 0
        self.parse_conf()

    def parse_conf(self):
        """parses the configuration file, interpreting every non-commented line
        as a directory into which wallpaper images reside.
        In case no images are found, the script exits"""
        self.bad_folders = []
        if not os.path.isfile(self.conf_file):
            with open(self.conf_file, 'w') as conf:
                self.append_error(conf, 'List your wallpapers folder here')
                print 'List your wallpapers folders in configuration file ', self.conf_file
                sys.exit(1)
        self.conf_last_modified = os.path.getmtime(self.conf_file)
        self.files = self.get_all_files()
        if not self.files:
            self.append_error(conf, 'No images found!')
            sys.exit(1)
        self.all_files = set(self.files)
        random.shuffle(self.files)

    def get_all_files(self):
        """adds all files in all directories found in the configuration file to
        a list containing all wallpapers to be shown with no duplicates (based
        on complete file name)"""
        files = []
        with open(self.conf_file, 'r+') as conf:
             # trim whitespaces and newlines
            for line in [x.strip() for x in conf.readlines()]:
                if not line.startswith('#'):
                    if os.path.isdir(line):
                        try:
                            files.extend([os.path.join(line, file) for file in os.listdir(line) if os.path.splitext(file)[1] in self.formats])
                        except OSError, e:
                            # deal with bad folders later...
                            self.bad_folders.append('%s: %s' % (line, e.strerror))
            if self.bad_folders:
                for folder in self.bad_folders:
                    self.append_error(conf, folder)
        return self.remove_duplicates(files)

    def remove_duplicates(self, files):
        seen = set()
        seen_add = seen.add
        return [x for x in files if x not in seen and not seen.add(x)]

    def append_error(self, conf, line):
        # go to the end of conf file and append messages there
        conf.seek(0, 2)
        conf.write('# %s - %s%s' % (strftime("%Y-%m-%d %H:%M:%S", gmtime()), line, os.linesep))

    def poll_for_new_files(self):
        """checks whether new files have been added to the configured folders"""
        all_files = set(self.get_all_files())
        new_files = all_files - self.all_files
        if new_files:
            shown = set(self.files[:self.index])
            self.files = list(all_files - shown)
            self.all_files = all_files
            random.shuffle(self.files)
            self.index = 0

    def run(self):
        sleep(self.delay) # this seems to be needed to avoid gnome-shell crashes
        while True:
            last_edit = os.path.getmtime(self.conf_file)
            if last_edit != self.conf_last_modified:
                self.parse_conf()
            next_bg = self.files[self.index]
            if os.path.isfile(next_bg):
                os.system('/usr/bin/gsettings set org.gnome.desktop.background picture-uri file://%s' % self.files[self.index])
                os.system('/usr/bin/gsettings set org.gnome.desktop.background picture-options %s' % self.mode)
                sleep(self.delay)
            self.index += 1
            self.poll_for_new_files()
            if self.index >= len(self.files):
                self.index = 0
                self.parse_conf() # this also checks that at least a bg exists!
                random.shuffle(self.files)

if __name__ == "__main__":
    changer = WallpaperChanger()
    changer.run()