None

None

In this tutorial, we'll represent an intentional missing value.

None represents "no value" or "nothing here yet".

middle_name = None

This does not mean the variable is missing. The variable exists, but its value is intentionally empty.

Why None Is Useful

Sometimes you need a placeholder before you know the real value:

selected_item = None

print(selected_item)

Later, the value can change:

selected_item = "Notebook"
print(selected_item)

Checking for None

Use is None to check for None:

middle_name = None

if middle_name is None:
    print("No middle name saved")
else:
    print(middle_name)

Use is not None for the opposite:

score = 0

if score is not None:
    print("Score recorded")

Notice that 0 is not the same as None. An empty score and a score of zero mean different things.

None Is Not a String

This is a string:

value = "None"

This is the special None value:

value = None

They are not the same.

Common Mistake

Do not compare to None with == while learning:

if value == None:
    print("Missing")

Prefer:

if value is None:
    print("Missing")

Practice

Create a variable called chosen_colour and set it to None. If it is None, print "Please choose a colour". Then assign it a colour and print it.