3C: Functions

Functions are a way to save time and energy by storing commonly used lines of code into one named set. For example, to text a friend, you could write multiple lines of code to do all of this:

Take out phone

Unlock phone

Open messaging app

Have I texted this friend before?

If yes, go to last text message with friend

If no, compose new message and add friend’s name

Write text message

Hit send

Or you could just use a function called  friend.text() at the beginning of every new program!

The first step to writing your own function is the term def. You are telling Python that you are “defining a function”.

Next comes your function name followed by parentheses and a colon. Your function name can be multiple words, but you need to add an underscore between every word. 

In this step, you are going to create your own function to have your CoDrone Mini fly in a square! Your function name will look like this:

def square():

Add a new indented line for the body of the function, and then write your square code below. You can use one of your old square programs if you saved it!

To run your function, write the function name underneath the function’s definition. If you don’t call the function, it won’t run!

def square():

    drone.takeoff()

    for i in range(1):

        drone.set_yaw(0)

        drone.set_pitch(30)

        drone.move(1)

        drone.set_pitch(0)

        drone.set_yaw(20)

        drone.move(2)

    drone.land()

square()

Import the CoDrone Mini and time libraries, create the drone object, and pair. Next, try running your code now. What happened?

After every function are parentheses, and this is where the parameters go. Parameters are variables the function needs to use, but not all functions will have parameters! In the previous example, you might have noticed that the function had an empty set of parentheses.

Think of a function as the processes part of a large factory. Some processes can run as-is. However, some processes need more information to run, like a program that will greet you personally by name!

For this activity, go back to the square program you just made and add two parameters in the parentheses: power and duration.

def square(power, duration)

Then you can change some of the parameters in your program:

def square(power, duration):

    drone.takeoff()

    for i in range(1):

        drone.set_yaw(0)

        drone.set_pitch(power)

        drone.move(duration)

        drone.set_pitch(0)

        drone.set_yaw(20)

        drone.move(2)

    drone.land()

square()

The power and time will be set when the function is called. For example, if you want the power to be set at 30 and the time for each command to be 1 second, then you would call your function in your main program like this:

square(30, 1)

Try running your program now. Did you notice anything different from when you had no parameters in your function?

A return function is slightly different from the functions you just saw. A return function returns a value or set of values. The values that are returned are called return values. Very creative, we know.

One real-life example of a return function is a calculator. You input an equation, and once you hit the equal sign, the calculator returns an answer! In this activity, your CoDrone Mini will simulate a calculator. After adding two numbers in the return function together, it will throttle up and down for the value of the answer.

After importing the CoDrone Mini and time libraries, creating the drone object, and pairing, define a function called  add  with x and y as parameters. Underneath, have the function return  x+y .

import CoDrone_mini

import time

drone = CoDrone_mini.CoDrone()

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()

Your program should look like this:

import CoDrone_mini

import time

drone = CoDrone_mini.CoDrone()

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:

import CoDrone_mini

import time

drone = CoDrone_mini.CoDrone()

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): “. Next, write an if statement so that if “q” is input, the program will break out of the loop. Create another variable called num2 and set its value to input() as well. Write “Input second number: ” in the parameters.

while True:

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

    if num1 == "q":

        break

    num2 = input("Input second number: ")

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:

import CoDrone_mini

import time

drone = CoDrone_mini.CoDrone()

drone.pair()


def add(x,y):

    return x+y


while True:

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

    if num1 == "q":

        break

    num2 = input("Input second number: ")

 
    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()

Challenge: Please Excuse My Dear Aunt Sally

You know how to add, but now try making functions for subtraction, multiplication, and division! Once you have that figured out, try adding parentheses and brackets to see if your CoDrone Mini can use the order of operations to solve your equation.

Hints:

• Subtraction sign: –
• Multiplication sign: *
• Division sign: /
• Exponent sign: ^