Upper Case error in simple code

Hi, my code keeps on showing me Upper case error. Why does it keeps on coming up on every command I save?

As the error says, this comes from Pylint which is an optional linter for Python code. The specific analyzer that is giving that warning is the invalid-name analyzer. You can completely disable Pylint or that specific analyzer if you do not want to see the warnings.

Basically a linter is trying to help make sure your code conforms to a certain style - naming conventions, documentation strings, etc. It should not prevent your program from running, but it does help keep codebases internally consistent.