print vs return

The #1 beginner trap: print shows a value on screen, while return hands it back to whoever called the function.

A function without return gives back None:

def bad(n):
    print(n * 2)    # shows it... then returns None
x = bad(5)          # x is None!

See it run

def shout(word):
    print(word.upper())

def loud(word):
    return word.upper()

a = shout("hi")
b = loud("hi")
print(a, b)

Two functions do the same work. Only one hands the result back.

Practice print vs return

Exercise 1

In the code editor below, double prints its answer instead of returning it, so result ends up None. Fix it so result is 10.

Exercise 2

Fix discount(price) so it returns the price with 20% off: discount(50) is 40.0. Showing the number with print inside the function is not enough. Prices are zero or more.

Exercise 3

Separate a conversion from its display: to_minutes(hours) returns hours * 60 and prints nothing. show_duration(hours) prints Duration: N min using that function and returns None. For whole-hour input, show an integer N. Set minutes to to_minutes(2), then call show_duration(2).

Exercise 4

Predict, then verify. Read this program before running it:

def shout(word):
    print(word.upper() + "!")

result = shout("hi")

What value does result hold? Guess, then run it, press Step through your code, and press Next until the label says Returning from shout(): the box shows what the call hands back. Set prediction to that value.

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Practice

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Visualizer Watch your code run line by line

Run your code, then choose Play to follow its execution.

Memory · names → values

Variables appear here as Python creates them.

Output & plots