Because if you read the function signature of a function like def fill_rectangle(color) you haven't got the slightest idea what valid values of "color" is. (Ign

Because if you read the function signature of a function like def fill_rectangle(color) you haven't got the slightest idea what valid values of "color" is. (Ignore the fact that python doesn't have types in the function signature to start with, say you're reading the documentation instead) If you knew that color was of the enum-type my_gui_lib.standard_colors you know exactly which colors you can use and you can reuse them for fill_ellipse also because it most likely uses the same type. Instead of every function having to reiterate all valid integer values of color or referring to some table. Your editor will also provide you with auto complete of valid values unless you're coding in notepad. In a type safe language you will even get compilation error if you provide a type/value out of range but since python is dynamic this would be hard. It's simply impossible to pass the function an invalid value, which is invaluable. So in python the value added isn't a strong as in a strong language but it's still there.