Lists

Have you ever made lists to keep track of your homework or your chores? You may have made separate lists for the tasks in each subject or divided your chores into categories. Many times in programming you will want to organize information. In Python, lists can be used to store and organize data of the same type without creating multiple variables. Because lists are able to do this, they are a data structure.

Here’s an example of a list:

subjects = ['algebra', 'english',   'robotics', 'history', 'biology']

Important: these lists are ordered lists. This means that 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]

Pretend that it’s Taco Tuesday and you need to come up with a shopping list so you can make tacos. After checking the kitchen, you come up with this list:

groceries = ['tortillas', 'meat', 'salsa', 'cheese', 'seasoning']

What if you forgot to add something to your shopping list? This is what makes a list a very useful data structure in Python. You can add information, delete information, and even reorder information. Below are nine useful methods for working with lists:

Append – Your family wants you to add vegetables, like lettuce, tomatoes, or onions. The append() method adds another item to the end of your list. Add vegetables to your list:

groceries.append('vegetables')

What do you think you will see if you print(groceries)? Try it out!

Insert – Since lists are ordered, you shop for your ingredients in order. What if you want to add sour cream to your list but you want to get it after the salsa and before the cheese? To insert an item, you need to know the list position you want the new item to occupy. Tortillas currently hold position 0, so sour cream would occupy position 3.The code to insert cheese at this position is groceries.insert(3, 'sour cream'). Note that the indices of all the following elements will be shifted by one. For example, seasoning used to be at position 4 but now it holds position 5:

groceries = ['tortillas', 'meat', 'salsa', 'sour cream', 'cheese', 'seasoning', 'vegetables']

Delete – Deleting an item from the list can be done with the delcommand. Like insert(), you need to know the index of the element that you want to delete. You find out that you already have cheese, so you remove it from the list with del groceries[4]. Note that the index of any following elements will shift down by one.

Remove – What if you did not know the index of the value you wanted to remove? Maybe your grocery list was too long and you could not find cheese on the list. Using groceries.remove('cheese')deletes the item without needing to know the index. Make sure you spell it right! If the list cannot find the value, it will not delete anything.

Length – You are now ready to checkout and you want to know if you can go into the express line, which only serves customers with 12 or fewer items. You’re in a hurry and you don’t want to count all of the items one by one. len()returns the number of items in your list.

print(len(groceries))

You can also assign this value to a variable and use it to automate whether or not you can go into the express line using an if statement:

num_items = len(groceries)

if (num_items < 13):
    print("Go to the express line!")
else:
    print("You have more than 12 items. No express line for you :(")

Clear – You arrive home from grocery shopping with everything you need so you want to empty your list. The clear()method removes all of the items from the list at once. You empty the list with groceries.clear()so that it’s ready for another Taco Tuesday.

There are three more operations that you will learn. These are separate from above because they deal will organizing the existing information in a list.

Sort – Suppose you have a list of students that attend a high school. It’s graduation time and you are asked to sort the list of students alphabetically for the ceremony. Calling the sort()method will sort the list of names alphabetically:

students = ['Gabriel', 'Jada', 'Isaiah', 'Ariana', 'Sebastian', 'Christina']
students.sort()
print(students)

Output:

['Ariana', 'Christina', 'Gabriel', 'Isaiah', 'Jada', 'Sebastian']

Sorted – If you use the sort()function, you cannot go back to the original order of the list! Luckily, there is an alternative to temporarily alter the list with sorted(). The difference between the two is that sort()changes the original list and sorted()creates a new list from the original.

Create your own list called studentswith the names of some friends or classmates. Then use the following code to see how this works.

print("Original:")
print(students)	# Prints original list

print("Sorted List:")
print(sorted(students))	# Prints the sorted list but does not modify original

print(students)	# Prints original, unsorted list

Since sorted()creates a new list, you can save that list to keep the sorted and unsorted lists separate. For example:

sorted_students = sorted(students)	# Create a new list to hold sorted values
print(students)	# Print original list
print(sorted_students)	# Print sorted list

Reverse – You can probably guess that this method reverses the list! You can use this method in conjunction with sort() or sorted()to sort a list in reverse alphabetical order.

sorted_students = ['Ariana', 'Christina', 'Gabriel', 'Isaiah', 'Jada', 'Sebastian']
sorted_students.reverse()
print(sorted_students)

Output:

['Sebastian', 'Jada', 'Isaiah', 'Gabriel', 'Christina', 'Ariana']

Now you will combine your knowledge of lists and LEDs to create a list of colors that you can cycle through to create all kinds of patterns.

You learned that instead of using the RGB values, the color can be set by one of the names listed in this document. This data type is called an enum, because the values are enumerated. This means that each color name is associated with a particular number. Think of each color as having an ID. This is how the computer knows which red, green, and blue values correspond to that name to produce the color.

Lists can hold enums as a data type. Create a list of your favorite colors:

my_favorite_colors = [CoDrone.Color.Coral, CoDrone.Color.Cyan, CoDrone.Color.Green,CoDrone.Color.Magenta, CoDrone.Color.Turquoise]

Accessing the elements in the list is the same as with strings and numbers.

You’re going to combine what you learned about LEDs in the last lesson to make a list and loop through it!

You are probably familiar with the acronym ROYGBIV to remember all the colors of the rainbow. Create a list called rainbow and populate it with the seven colors:

rainbow = [Color.Red, Color.Orange, Color.Yellow, Color.Green, Color.Blue, Color.Indigo, Color.Violet]

Next, set up your loop. Remember that there are 7 colors in your list and counting starts at 0. We set all of our LEDs to stay solid at a brightness level of 100, but you can set whatever pattern and interval or brightness that you want. Make sure you include a command that holds the LEDs for half a second so you can actually see them!

for i in range(0,7):
    drone.set_all_led(rainbow[i], SOLID, 100) # Initial color + where we are in the rainbow
    sleep(0.5)	# Hold color for .5 sec

Add pairing, libraries, and an end command. This is what your final program should look like!

import CoDrone
from time import sleep
from CoDrone import Color	# This shortens CoDrone.Color.Red to Color.Red

drone = CoDrone.CoDrone()
drone.pair()# Color list

rainbow = [Color.Red, Color.Orange, Color.Yellow, Color.Green, Color.Blue, Color.Indigo, Color.Violet]

for i in range(0,7):	# There are 7 colors # Variable 'i' represents current step in rainbow
    drone.set_all_led(rainbow[i], SOLID, 100) # Initial color + where we are in the rainbow
    sleep(0.5)	# Hold color for .5 sec

drone.close()

Challenge: Multiple Rainbows

You know how to loop through a rainbow list once. Now try multiple times!

Rules:

• One program should use nested for loops to have the rainbow loop three times
• One program should loop the rainbow infinitely

Triple Rainbow Solution:

import CoDrone
from time import sleep
from CoDrone import Color # This shortens CoDrone.Color.Red to Color.Red

drone = CoDrone.CoDrone()
drone.pair()

# Color list
rainbow = [Color.Red, Color.Orange, Color.Yellow, Color.Green, Color.Blue, Color.Indigo, Color.Violet]
for i in range (0,3): # There are 3 iterations (rainbows)
    for j in range(0,7):	# There are 7 colors # Variable 'j' represents current step in rainbow
        drone.set_all_led(rainbow[i], SOLID, 100)
        sleep(0.5)	# Hold color for .5 sec

drone.close()

Infinite Rainbow Solution:

import CoDrone
from time import sleep
from CoDrone import Color # This shortens CoDrone.Color.Red to Color.Red

drone = CoDrone.CoDrone()
drone.pair()

# Color list
rainbow = [Color.Red, Color.Orange, Color.Yellow, Color.Green, Color.Blue, Color.Indigo, Color.Violet]

while True: # Run forever
    drone.set_all_led(rainbow[i], SOLID, 100) # Initial color + where we are in the rainbow
    sleep(0.5)	# Hold color for .5 sec

drone.close()