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Introduction to Functions

So far, we have only seen functions that print out some result to the console. Functions can also return a value to the user so that this value can be modified or used later. When there is a result from a function that can be stored in a variable, it is called a returned function value. We use the keyword return to do this.

Here’s an example of a function divide_by_four that takes an integer argument, divides it by four, and returns the result:

def divide_by_four(input_number): return input_number/4

The program that calls divide_by_four can then use the result later:

result = divide_by_four(16) # result now holds 4 print("16 divided by 4 is " + str(result) + "!") result2 = divide_by_four(result) print(str(result) + " divided by 4 is " + str(result2) + "!")

This would print out:

16 divided by 4 is 4! 4 divided by 4 is 1!

In this example, we returned a number, but we could also return a String:

def create_special_string(special_item): return "Our special is " + special_item + "." special_string = create_special_string("banana yogurt") print(special_string)
Our special is banana yogurt.



The function calculate_age in creates a variable called age that is the difference between the current year, and a birth year, both of which are inputs of the function. Add a line to return age.


Outside of the function, call calculate_age with values 2049 (current_year) and 1993 (birth_year) and save the value to a variable called my_age.


Call calculate_age with values 2049 (current_year) and 1953 (birth_year) and save the value to a variable called dads_age.

Print the string "I am X years old and my dad is Y years old" to the console, with my_age where the X is and dads_age where the Y is.

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