I spent 5 hours getting this working just now after trying all of these other solutions under the sun, so let me finally put this to rest.
Note: This is for raspbian, with main user account using the default username ("pi")
Here are the steps in order:
Name your python file main.py and drag your python file to the desktop.
Next, create a new plain text file and add the following contents:
#!/bin/bash
python3 /home/pi/Desktop/main.py
Save this text file as launch.command on the desktop. This is shell script to launch your python file. By default it won't work, we have to chmod it (next step)
Run terminal and run the following command:
chmod u+x /home/pi/Desktop/launch.command
Now double clicking launch.command (and selecting execute) will launch your python file.
At this point, we are ready to get it launching on boot. If you've done any other launch attempts prior to this please undo all of those file changes you had done.
Open terminal and run the following:
sudo nano /etc/systemd/system/myproject.service
We are just going to call it myproject for now, don't change any of this until after you get it working, then feel free to attempt a rename
In the window that pops up, copy paste the following exactly:
[Unit]
Description=Start Myproject
After=graphical.target
Wants=graphical.target
[Service]
User=pi
Group=pi
ExecStart=/bin/bash -c "export DISPLAY=:0; export XAUTHORITY=/home/pi/.Xauthority; /home/pi/Desktop/launch.command"
[Install]
WantedBy=graphical.target
Now press ctrl+x to exit-and-save, it will prompt you to save changes, type "y", the filename should already be entered as .../myproject.service, if it is then press enter and it will save and exit, if the file name is blank it messed up (this just happens sometimes), quit terminal and try all of this again, sorry.
Now in terminal enter:
sudo systemctl daemon-reload
Then
sudo systemctl enable myproject.service
Lastly
sudo reboot
On launch, before anything else shows (after the boot up splash screen shows of course, but before desktop shows) your GUI will now launch, congrats!
I recommend you launch it full screen, to do that edit your python file to use this:
root.attributes('-fullscreen', True)
NOTE, 'root' is likely not what you called your TK() init.... at the end of your code you have something like XXXX.mainloop(), change 'root' to whatever XXXX is, stick this right after your init of TK()
Once you've reboot, you are likely stuck in the app (especially if you launched it full screen), things like alt+f4 or alt+f11 won't kill your program. To exit, press the windows/menu button on your keyboard, the access panel will appear you and can go to accessories>terminal to launch a new terminal window, then run the following:
sudo systemctl stop myproject.service
The program will be killed and you will be back to your standard desktop...
NOW, to prevent it from launching again on bootup, simply rename your launch.command file to DISABLED_launch.command and when you're ready to start launching on bootup again set the name back.
Go get a drink, you've earned it.
Also, you can obviously put these places other than desktop but MAKE SURE you always use the full path in any of these commands, don't use the '~/..' shortcut.
