Functions that return an answer

The idea

A function gives a reusable operation a name. def starts the definition, parentheses list the input parameters, and an indented body contains the work. Defining the function does not run its body; calling the function with arguments runs it with those input values.

return sends a result back to the caller and ends that function call. The caller can save the result, use it in another expression, or print it. print displays something for a person; it does not replace returning the value another calculation needs.

Begin with a small function that uses only its parameters. Test two different calls and an edge case such as a quantity of zero. Local parameter names are filled separately for each call. Lists and default parameters introduce additional state rules; those come later in Functions and dependable defaults.

def line_total(price, quantity):
    return price * quantity

first = line_total(4, 3)
second = line_total(4, 0)
print(first)
print(second)

12
0

Each call supplies its own arguments. The function returns a number, and printing is the caller’s separate choice.