2.3: Return Functions

Goals:

By the end of this lesson, I will be able to:

1. Explain the difference between return and void functions
2. Describe when return functions should be used in a program
3. Describe when void functions should be used in a program
4. Create a return function and use its output to influence the program

Steps to Success:

1. Return Functions
2. Final Code
3. Return Functions with User Input
4. Final Code
5. Challenge: Conversion Calculator

A return function is slightly different from the functions you have seen in the previous lesson. A return function returns a value or set of values. Let’s see how we can use return functions to create an inch to centimeter conversion calculator:

Now we know how to create a very basic calculator! In this activity, your CoDrone EDU will simulate a calculator. After adding two numbers together in the return function, it will throttle up and down for the value of the answer.

After importing the time library, define a function called  add  with x and y as parameters. Underneath, have the function return  x+y.

from codrone_edu.drone import *

import time

drone = Drone()

drone.pair()


def add(x,y):

    return x+y

Create a variable called  answer that will store the return function. Next, include a print command that will display “The answer is” along with the answer. 

answer = add(2, 3)

print("The answer is ", answer)

Program your drone to take off, and then create a for loop with answer as its parameter. Within the loop, have the drone throttle up for half a second at 30% power, and then down for the same amount of time and power. Finally, have the drone land.

drone.takeoff()

for i in range(answer):

    drone.set_throttle(30)

    drone.move(0.5)

    drone.set_throttle(-30)

    drone.move(0.5)
 
drone.land()

drone.close()

Your program should look like this:

from codrone_edu.drone import *

import time

drone = Drone()

drone.pair()


def add(x,y):

    return x+y


answer = add(2, 3)

print("The answer is ", answer)

drone.takeoff()

for i in range(answer):

    drone.set_throttle(30)

    drone.move(0.5)

    drone.set_throttle(-30)

    drone.move(0.5)

drone.land()

Try this out with multiple numbers! What happens when your drone gets to bigger numbers?

In this step, you’re going to take the calculator simulation even further by having a user input the numbers to add together!

Keep the first portion of your program the same:

from codrone_edu.drone import *

import time

drone = Drone()

drone.pair()


def add(x,y):

    return x+y

Set up a while loop so that while true the program will run. Inside the loop, create a variable called  num1 and set its value to  input(). In the input parameters, write “Input first number (or q to quit): “. Create another variable called num2 and set its value to input() as well. Write “Input second number (or q to quit): ” in the parameters. Next, write an if statement so that if “q” is input, the program will break out of the loop if num1 or num2 is “q”.

while True:

    num1 = input("Input first number (or q to quit): ")

    num2 = input("Input second number (or q to quit): ")

    if num1 == "q" or num2 == "q":
        break

While still in the while loop, create a variable called  answer that will use the  add(x,y) function to return the sum of num1 and num2. Next, include a print command that will print the answer.

answer = add(int(num1), int(num2))

print("The answer is ", answer)

The rest of your program will be the same!

drone.takeoff()

    for i in range(answer):

        drone.set_throttle(30)

        drone.move(0.5)

        drone.set_throttle(-30)

        drone.move(0.5)

    drone.land()

Your final program should look like this:

from codrone_edu.drone import *

import time

drone = Drone()

drone.pair()


def add(x,y):

    return x+y


while True:

    num1 = input("Input first number (or q to quit): ")

    num2 = input("Input second number (or q to quit): ")

    if num1 == "q" or num2 == "q":      
        break
 
    answer = add(int(num1), int(num2))

    print("The answer is ", answer)

    drone.takeoff()

    for i in range(answer):

        drone.set_throttle(30)

        drone.move(0.5)

        drone.set_throttle(-30)

        drone.move(0.5)

    drone.land()

drone.close()

Many countries and systems use different ways of measuring quantities such as distance, mass, force, etc…  For this exercise, you will create a conversion calculator that takes in 4 different measurements and converts them to a different measurement. For example, we created a conversion function for inches to centimeters earlier in the lesson. You can choose any conversions you would like. To successfully complete this challenge, your program must:

1. Have a list that contains the abbreviations a user will choose from for the measurement to be converted
2. Prompt for 2 input values, the amount, and measurement
3. Have a function that takes in the two input values and returns the calculated value and measurement as a string
4. Store the result as a variable
5. Print the result in a sentence that tells the user what they input and what the result was (For example: “You entered 5 inches, which is 12.7 centimeters”)

A few notes:

• You can add strings together by using the + sign
  • print(“Hello” + “World”) will print “Hello World”
• You can do the same for variables and strings:
  • name = John
  • print(“Hello” + name) will print “Hello John”

In this lesson, you learned about return functions. You learned how they differ from void functions, when you should use return functions in a program, and how their outputs can be used with your program.