How to organize a project in Python, with a base and a custom part?

Question

Python

There is a certain application that acts as the Core of the system. Work with the database, authorization, work with files, some tools and so on are stuffed there.
In the folder tree of this application, at the very top level, there is a Custom folder. When you need to stir up a new project, so as not to create everything anew, all the work to create a new highly specialized functionality goes in this folder.
Now I do this, I clone the Core from git and add the files to the Custom folder by simply copying the files from the narrow project folder. It turns out this type of deployment.
I look at it and I don't like it. There are already several projects. The core is developing, projects too. You need to keep everything up to date.
I don’t want to branch into git, soon a project will be branched off, which I will not control, and the Core will need to be updated.
How to organize this work?

Answer 1

1. Section of the official documentation about modules and packages .
   
2. Section of the official documentation about the preparation of distributed distributions .