The of ( : ) what does it do?

[deanhystad]

You guessed wrong. In "protein: Nutrient = Nutrient(name="Protein")" the colon is used in a type hint, not in a dictionary.

protein is a variable. It is assigned the value Nutrient(name="Protein"). The assignment has a type hint telling the reader that Nutrient(name="Protein") returns an instance of class "Nutrient".

variable : type_hint = value
protien : Nutrient = Nutrient(name="Protein")

The code does exactly the same thing if you leave the type hint out.

protien = Nutrient(name="Protein")