User Input

In the last lesson, you learned how to define and call functions with different parameters. In this lesson, you will learn how to change the input parameters by typing them in with your keyboard! Python includes a function input() that reads the keyboard input and returns a string. For example:

my name = input("What is your name?")

When you hit enter, any input that you typed in will be saved as a string in my_name.

Just like you saw in the last step, you can assign variables to messages and print the statement by referencing the variable:

message = "CoDrones can fly!"
print(message)

You can even print two strings in the same line:

first_word = "base"
second_word = "ball"
print(first_word, second_word)

Did you notice that there’s a space between each string? The way to avoid this is called concatenation, and it’s a fancy name to describe combining strings. You use the + operator to concatenate strings:

first_word = "base"
second_word = "ball"
compound_word = first_word + second_word
print(compound_word)

Your output should be:

baseball

What if you want to combine two variable types in a print statement? What do you think the output will be?

seconds = 3
print("My CoDrone hovered for " + seconds + "seconds.")

Oh no, you got an error! You can only concatenate string types in Python, and seconds is an int data type. There are two ways to solve this problem. The first is called type casting, which is when one data type is converted into another.

• str() converts data to a string
• int() converts data to an int
• float() converts the data to a float

To print the statement above, you need to type cast the variable seconds to a string within your print statement:

seconds = 3
print("My CoDrone hovered for " + str(seconds) + "seconds.")

Test the string out again. Did you get any errors this time?

The second way to avoid type errors is to use the %, or modulus, operator in Python. When used with integers the modulus operator returns the remainder, but with strings it is used to format output.

Think of the modulus operator as a placeholder for your variables in the string. The notation will depend on what kind of data the placeholder represents:

• %s – placeholder for a string
• %i – placeholder for an integer
• %f – placeholder for a float

To print an int variable within a string, replace the seconds variable with %i.

seconds = 5
print("My CoDrone hovered for %i seconds." % (seconds))

When using modulus, you need to provide the variables that the program should insert into the print statement after your string. This same idea works for more than one variable:

seconds = 5
times = 3
print("My CoDrone will takeoff, hover %i seconds, and land %i times!" % (seconds, times))

Try concatenation and modulus out so your program can respond to you with a personalized greeting!

my_name = input("What is your name?")
print("Hello, " + my_name)

my_name = input("What is your name?")
print(“Hello, %s” % my_name)

Next, come up with some other questions and phrases so that you can have a “conversation” with the computer!

In the last lesson you should have come up with functions for different flight movements. In this lesson, you are going to create a menu of options and use input() to select which function you want to run. This is one example:

Menu:
1. Fly in a square
2. Fly in a triangle
3. Spin in place
4. Exit

The menu will be displayed after each command until you select “Exit”. This task is going to combine all of your knowledge on input, formatting output, functions, and loops!

First, you will need to define the display_menu() function that prints the menu to the screen.

def display_menu():
    print("\tMenu")
    print("1. Fly in a square\n" +
        "2. Fly in a triangle\n" +
        "3. Spin in place\n" +
        "4. Exit")

The long string was broken up using the concatenation operator to avoid using multiple print statements. Remember to line up the following lines at the next indent as shown so you don’t get an indentation error!

For the main program, the program needs to be able to read user input and determine which function to execute. You will use if statements to check if the input is “1”, “2”, “3”, or “4”.

Create a variable called option and assign it to input().

option = input("Pick an option 1-4:")

Depending on the input, the drone will fly a different pattern! What kind of statement would be ideal for checking all of the cases? If statements! Write if and elif statements for the first three options:

if option == "1":
    square()
elif option == "2":
    triangle()
elif option == "3":
    spin()

You will need to define all of the functions yourself before your main program. You can also use your own pre- defined functions from the last lesson.

There is one more menu option leh to quit the program. Do you remember how to quit a while loop? Use the break statement!

elif option == "4":
    break

So far your program should look something like this:

def square():
    # Code

def triangle():
    # Code

def spin():
    #Code

def display_menu():
    print("\tMenu")
    print("1. Fly in a square\n" +
        "2. Fly in a triangle\n" +
        "3. Spin in place\n" +
        "4. Exit")

while True:

    display_menu()
    option = input("Pick an option 1-4: ")

    if option == "1":
        square()	
    elif option ==	"2":
        triangle()	
    elif option ==	"3":
        spin()	
    elif option ==	"4":
        break

In this example, the program will not give an error if you do not give an appropriate answer. However, it is always a good idea to handle every case possible. Include an error message that you can customize however you want!

else:
    print("That is not an option. Try again!")

For more practice with input, you are going to modify the program you just made! Aher selecting an option, each option will ask for more information to complete the task. For example, modify the square() definition to take in parameters for pitch value and move() value:

def square(power, seconds):
    for i in range(0,4):
        drone.set_pitch(power)
        drone.move(seconds)
        drone.set_yaw(power)
        drone.move(seconds)

This function now has parameters for power and time. You will need to get more user input to assign these values inside of each if statement. Remember that the input is saved as a string! Even though you are typing in a number, you will need to use the type casting technique to represent the variable as an integer. Here is an example of type casting:

power = int(input("What is the pitch value?"))
seconds = int(input("What is the move() value?"))

The variables now hold integer values that can be passed into the square() function!

while True:
    display_menu()
    option = input("Pick an option 1-4:")

    if option == "1":
        power = int(input("What is the pitch value? "))
        seconds = int(input("What is the move() value? "))
        square(power, seconds)

As an activity, try modifying all of your other functions to have parameters set by user input. Keep in mind the data type that the function needs and type cast the input correctly!

Challenge: Remote Control

Use what you just learned to turn your keyboard into a remote control!

Rules:

• Each flight direction should have its own key, so you should have separate functions for roll right, roll left, pitch forward, pitch backward, yaw right, yaw left, throttle up, and throttle down.
• Include a menu option to exit the program.