404 - Abstract Base Classes not Found

So I was going through this repository and I found (to what I went through, and I didn't go thoroughly) that there isn't anything regarding Abstract Base Classes, even though they are quite an important aspect of Object-Oriented Programming.
In lieu of this, I suggest that both the code and an explanation should be added in here.
I myself have come up with the solution and I'll be making a pull request soon. However, others are encouraged to add something of the sort, and it might turn out better than what I come up with. Peace ✌🏻