I have created an extremely simple demo program written in Tkinter - Python showing a simple GUI, and building a snap install file using Snapcraft.
I have put a video on you tube HERE showing the steps you need to get this working.
You can download a zip of all the needed files HERE as well is the simple GUI used.
It is all very simple once you know how.
You put your simple Python code in a folder called 'bin' then edit some config files to give the name of your program, your name and email, and that's about it.
The files you need to edit are 'snapcraft.yaml' stored in a folder called 'snap' '__init__.py' also one called 'README.md' another called 'requirements.txt' and finally one called 'setup.py'.
These are all included in the zip file you can download above.
Change the needed parts to include your personal details, and upload it all to git hub, and you can build your first snap file by simply going into the folder on your computer that holds the local copy of your creation and giving the command snapcraft
more details are in the zip file.