watch function header tutorial and apply lessons

[jschalk]

• [ ] watch https://www.youtube.com/watch?v=WI6CqykFbDc
• [ ] consider what should be changed in jaar

[jschalk]

• [x] function naming
• [x] function arguments
• [x] function default arguments
• [x] args kwargs arguments
• [x] options object
• [x] return type
• [ ] making your function more generic

[jschalk]

• [ ] consider adding return None to methods and functions that don't return anything.