Implementing custom trendlines similiar to graphing.py

Question

I am currently doing the exercise named "Exercise - Implement supervised learning" in the learning path "Build classical machine learning models with supervised learning" in Microsoft Learn and encountered the name graphing.py uploaded by the people of Microsoft Learn.

I was not able to use the graphing.py's function, that is, scatter_2D. Two errors appeared,

1. AttributeError: 'NoneType' object has no attribute 'index'
2. KeyError: None

Is there any other way i can draw a custom trendline (that is a function) onto another notebook that is not Microsoft Learn Sandbox? Thank you in advance.