2.2: Lists

Goals:

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

1. Explain the value of lists and how they are used in programs
2. Define what a data structure is and why it is different than single value variables
3. Explain how to select items from a list
4. Describe what an index is and why index values start at 0
5. Create a program the uses lists to make decisions
6. Play notes from the CoDrone EDU‘s buzzer
7. Traverse (move through) a list using loops and the list length

Steps to Success:

1. What are Lists?
2. Play a Note
3. Make a List
4. Get the Length of Your List
5. Lists and Loops
6. Additional Lists
7. Challenge 1: Make a Ringtone
8. Challenge 2: Light Show

Making lists is a way for us to organize information. Some lists can be ordered, such as a list of books you own in alphabetical order. Other lists can be unordered, such as a grocery list or to do list. Either way, keeping a list of items together makes it easier to access information.

In Python, lists store and organize data of the same type without you having to create multiple variables. For example, this list could represent your classes:

subjects = ['algebra', 'english',  'computer science', 'history', 'biology']

Each item has a position in the list called the index, which is an integer that refers to its position in the list starting from 0. The first element in the list is at index 0 because it is 0 steps away from the beginning of the list. In any case that involves counting, you will be starting from 0, so don’t forget!

Having an index is like having the address of where your information lives. A particular value can be accessed by the name of the list and its index:

listName[index]

Now that we know a little about lists, let’s take a look at an example of how to use lists in a program:

To explain lists, we’re going to be using the buzzer on your CoDrone EDU’s controller! Since musical notes are part of groups called scales, you will be able to hear your lists in action.

The first thing you need to do is play one note. Import the CoDrone EDU and note libraries, create the drone object, and pair to your CoDrone EDU. Next, play the note! The first parameter is the note itself, and the second parameter is how many seconds it will play for. We used middle C for our program, but you can use whatever note you like.

Try this out and see what the note sounds like!

from codrone_edu.drone import *

drone = Drone()
drone.pair()

drone.drone_buzzer(Note.C4, 500)

Now that you’ve made some music with the controller, let’s get back to lists.

In music, scales are groups of eight notes that increase or decrease in pitch, and they typically start with a C note. What you will be doing in this activity is making a list of notes for a C-major scale and then using that list to play specific notes.

After importing the CoDrone EDU and note libraries, creating the drone object, and pairing to CoDrone EDU, create a list called  notes . Next, add in the notes for your scale. Your scale can start with C3, C4, C5, C6, or C7, and then go all the way up or down to the next octave, or the note that’s 8 steps away from the first note.

notes = [Note.C3, Note.D3, Note.E3, Note.F3, Note.G3, Note.A3, Note.B3, Note.C4]

Once the list is finished, you can practice playing a specific note from the list. This is what that line of code will look like:

drone.drone_buzzer(notes[0], 500) # change the index to change notes

Remember that counting starts at 0, so  notes[0] will play the first note,  notes[1] will play the second, and so on.

This is what your program should look like:

from codrone_edu.drone import *

drone = Drone()

drone.pair()
notes = [Note.C3, Note.D3, Note.E3, Note.F3, Note.G3, Note.A3, Note.B3, Note.C4]
drone.drone_buzzer(notes[0], 500) # change the index to change notes

Lists can be long, and there may be times when you forget how many items your list has! To help with this, you can use the  len() function. It will print out the number of items in your list.

Try it out by using print(len(notes))after your list in your last program. Does your list have the correct amount of items?

Your program should look something like this:

from codrone_edu.drone import *

drone = Drone()

drone.pair()

notes = [Note.C3, Note.D3, Note.E3, Note.F3, Note.G3, Note.A3, Note.B3, Note.C4]

print(len(notes))

You can use a loop to play every note in your list one time for 0.5 seconds. To do this, use your code from the last step, but take out the print command. 

Use a for loop that will access the length of the notes list and then play them for 0.5 seconds each. Since the range of the for loop is the length of the list, each note will play only one time. 

This is what your program should look like:

from codrone_edu.drone import *

drone = Drone()

drone.pair()

notes = [Note.C3, Note.D3, Note.E3, Note.F3, Note.G3, Note.A3, Note.B3, Note.C4]

for i in range(len(notes)):
    drone.drone_buzzer(notes[i], 500)
    time.sleep(0.1)

Just like variables, you can have more than one list in your program! These are great to have if you have different data types or want to keep your items categorized. For this step, you will be adding another list for note duration.

Use your program from the last step and then create a list called  duration . This list should be the same size as the notes list, so include eight note durations. They can all be different, or some can be the same. Just remember that these durations are in seconds.

Next, add a for loop to play both the notes and their durations, and then run your program to see what it sounds like! You can always add or subtract items from their lists. Just make sure you have the same amount of items in both.

Your program should look something like this:

from codrone_edu.drone import *

drone = Drone()

drone.pair()


notes = [Note.C3, Note.D3, Note.E3, Note.F3, Note.G3, Note.A3, Note.B3, Note.C4]

duration = [100, 100, 250, 250, 250, 100, 100, 500]


for i in range(len(notes)):
    drone.drone_buzzer(notes[i], duration[i])

Now that we can make progressions of notes, try to create your own ringtone! Make sure your program meets the following requirements:

1. Ringtone must last at least 10 seconds
2. Use at least 2 lists
3. Use at least 5 different notes
4. Use at least 2 durations for the notes

Advanced: See if you can use a for or while loop outside of your for loop where the notes play to make your ringtone repeat the whole sequence of notes multiple times.

For this challenge, we will use our knowledge of LEDs to make a light show with our drone. To complete this challenge your drone should do the following:

1. Create a list of color names (strings)
2. Loop through the list
3. Change the drone LED to the appropriate color based on the list of colors.
4. Have different durations for each step in the show
5. Run for at least 10 seconds

In this lesson, you learn about the concept of lists! Lists can be used to store many values of the same data type and those values can be accessed using index values. You also learned how to use the CoDrone EDU’s buzzer and program it using lists!