Yes, @Invisibleman. Python uses None, rather than null though.

Very nice, but it is better not to use such code in production

Great use of OOP concepts

Also, please mark discussion of code with a spoiler flag (I just added one to your comment).

I have figured out the problem, but I have to delete it first. How? The Delete button is not working.

Voile - Perhaps each task is a slightly disguised version of the other task.

This is basically a slightly disguised version of inverse triangular number + triangular row sum. There are already duplicates on each part of the task.

Blind4Basics - This is the task condition.

I did, please see.

raulbc777 had already made many such katas, so please unpublish before it gets retired plus the issues below.

Please tell me how to create a random test, show an example, please

If you need help creating a Python kata, you can find some help here: https://docs.codewars.com/languages/python/authoring

Before publishing the kata again, make sure your kata conforms to authoring guidelines: https://docs.codewars.com/authoring/guidelines

If you do not understand something, need any help, or have any further questions, you can ask them in #help-author channel of Codewars Discord. You can also share a link to a draft of your kata (before publishing) in the #review channel of the said Discord server for a preliminary review.

Sample tests are missing it blocks.
Cannot check full test because the kata cannot be completed now.