None

Why Use None?

Let's say we have a variable a = None. Why would we ever want to do this?

Imagine you are developing a course. When a student first starts, before they have taken a test or turned in an assignment, their grade isn't $0$ (because they haven't failed yet) and it isn't $100$ (because they haven't earned it yet). Their grade is effectively "nothing."

In this situation, we use grade = None until we have an actual result to enter into the variable.

Try it out:

• Print grade.
• Print grade type.

By using None, you tell the program that the variable exists, but it doesn't have a value yet.

Exercise 1: The New Enrollment

A new student has just joined the school database. They exist in the system, but since they haven't attended any classes yet, they don't have a GPA.

• Task: Create a variable named student_gpa and assign it the value of None.
• Goal: Print the variable and its type() to confirm it is a NoneType.

Exercise 2: The Return Value Mystery

Some list methods don't return a new list; they just change the original and return "nothing." Let's see this in action.

• Starting List: colors = ['red', 'blue', 'green']
• Task: Create a variable called result and set it equal to colors.append('yellow').
• Goal: Print result. Observe that even though the color was added to the list, the action itself returned None.

Exercise 3: The Placeholder Logic

In programming, we often check if a variable is still "empty" before we perform a calculation.

• Task: Create a variable final_score and set it to None.
• Task: On the next line, re-assign final_score to a number of your choice.
• Goal: Print final_score to show how it transitioned from "nothing" to a value.