Start Lock Screen menu item for Caja on Desktop (solution to https://ubuntu-mate.community/t/how-to-change-the-menu-right-click-on-the-desktop-from-ubuntu-mate-20-04/24561)

startlockscreencaja.py

# -*- coding: utf-8 -*-
# Start Lock Screen menu item for Caja, shown only on ~/Desktop
# 
# Copyleft 2021, Norbert
#
# Based on dejadup.py from deja-dup-caja deb-package.

import subprocess, os
# Python 2 or 3
try:
    from urllib import unquote
except ImportError:
    from urllib.parse import unquote

from gi.repository import Caja, GObject

class StartLockScreen:
    def __init__(self):
        pass
    
    def _run_cmd(self, cmd, background=True):
        """Run command into shell"""
        if background:
            proc = subprocess.Popen(cmd, shell=False)
        else:
            proc = subprocess.Popen(cmd, shell=False, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
            stdout,stderr = proc.communicate()
            return stdout,stderr
    
    def restore_missing(self, item):
        """Lock session call"""
        self._run_cmd(['mate-screensaver-command', '--lock'], background=True)

class Utils:
    def __init__(self):
        pass
    
    def get_filepath(self, items):
        """Get just the path from a complete path and filename"""
        try:
            item = items[0]
        except:
            item = items
        return unquote(item.get_uri()[7:])

class StartLockScreenCaja(GObject.GObject, Caja.MenuProvider):
    def __init__(self):
        self.startlockscreen = StartLockScreen()
        self.utils = Utils()

    def _missing_activate(self, menu, item):
        """Missing items"""
        self.startlockscreen.restore_missing(item)
    
    def get_background_items(self, window, current_folder):
        """Caja invoke this when user clicks in an empty area"""
        Menu = Caja.MenuItem(
                name="StartLockScreen::Start",
                label="Start Lock Screen",
                icon="system-lock-screen")
        
        # Get complete path
        item = self.utils.get_filepath(current_folder)
        
        if item == "desktop:///":
            Menu.connect('activate', self._missing_activate, item)
            return [Menu]