What is PEP 8?
style guide for Python https://www.python.org/dev/peps/pep-0008/
pep8 is a tool to check your Python code against some of the style conventions in PEP 8. Pep8 is a coding standard and Style Guide for readability and long-term maintainability. It's not a requirement for your code to work, just a good coding practice you should follow.
BMI calculator code project
How to create a border
Overloading + operator