Return Ends the Function

return does two things at once: it gives a value back, and it ends the function immediately. The rest of the function doesn't run:

def add(a, b):
    return a + b
    print("This line never runs.")

print(add(2, 3))

This prints:

5

The line after return never runs, because the function ended one line earlier.

This is handy together with conditions. The following function describes the weather based on the temperature:

def describe_weather(degrees):
    if degrees < 0:
        return "freezing"
    if degrees < 20:
        return "cool"
    return "warm"

print(describe_weather(-5))
print(describe_weather(12))
print(describe_weather(25))

This prints:

freezing
cool
warm

Let's follow the three calls:

• describe_weather(-5): -5 < 0 is True, so the function returns "freezing" and ends. The second condition is never checked.
• describe_weather(12): the first condition is False and the second one is True, so the function returns "cool".
• describe_weather(25): neither condition is True, so the function gets all the way to the last line and returns "warm".

We didn't need any elif or else: once a return runs, the rest of the function is skipped anyway. (With elif and else, the function would work the same.) But the order of the conditions matters, because the first return that runs wins. If the function checked degrees < 20 first, it would return "cool" for -5, since -5 is less than 20 too.