Lesson Objectives

After this lesson, you will be able to…

• Create lists in Python.
• Print out specific elements in a list.
• Perform common list operations.

What is a List?

Variables hold one item.

my_color = "red"
my_peer = "Brandi"

Lists hold multiple items - and lists can hold anything.

# Declaring lists
colors = ["red", "yellow", "green"]
my_class = ["Brandi", "Zoe", "Steve", "Aleksander", "Dasha"]

# Strings
colors = ["red", "yellow", "green"]

# Numbers
my_nums = [4, 7, 9, 1, 4]

# Both!
my_nums = ["red", 7, "yellow", 1, 4]

Accessing Elements

List Index means the location of something (an element) in the list.

List indexes start counting at 0!

my_class = ["Brandi", "Zoe", "Steve", "Aleksander", "Dasha"]
print(my_class[0]) # Prints "Brandi"
print(my_class[1]) # Prints "Zoe"
print(my_class[4]) # Prints "Dasha"

We Do: Lists

1. Create a list with the names "Holly", "Juan", and "Ming".
2. Print the third name.
3. Create a list with the numbers 2,4, 6, and 8.
4. Print the first number.

List Operations - Length

len():

• A built in list operation.
• How long is the list?

# length_variable = len(your_list)

my_class = ["Brandi", "Zoe", "Steve", "Aleksander", "Dasha"]
num_students = len(my_class)
print("There are", num_students, "students in the class")
# => 5

Adding Elements: Append

.append():

• A built in list operation.
• Adds to the end of the list.
• Takes any element.

# your_list.append(item)

my_class = ["Brandi", "Zoe", "Steve", "Aleksander", "Dasha"]
my_class.append("Sonyl")
print(my_class)
# => ["Brandi", "Zoe", "Steve", "Aleksander", "Dasha", "Sonyl"]

Adding Elements: Insert

.insert():

• A built in list operation.
• Adds to any point in the list
• Takes any element and an index.

# your_list.insert(index, item)

my_class = ["Brandi", "Zoe", "Steve", "Aleksander", "Dasha", "Sonyl"]
my_class.insert(1, "Sanju")
print(my_class)
# => ["Brandi", "Sanju", "Zoe", "Steve", "Aleksander", "Dasha", "Sonyl"]

Removing elements - Pop

.pop():

• A built in list operation.
• Removes an item from the end of the list.

# your_list.pop()

my_class = ["Brandi", "Zoe", "Steve", "Aleksander", "Dasha", "Sonyl"]
student_that_left = my_class.pop()
print("The student", student_that_left, "has left the class.")
# => "Sonyl"
print(my_class)
# => ["Brandi", "Zoe", "Steve", "Aleksander", "Dasha"]

Removing elements - Pop(index)

.pop(index):

• A built in list operation.
• Removes an item from the list.
• Can take an index.

# your_list.pop(index)

my_class = ["Brandi", "Zoe", "Steve", "Aleksander", "Dasha", "Sonyl"]
student_that_left = my_class.pop(2) # Remember to count from 0!
print("The student", student_that_left, "has left the class.")
# => "Steve"
print(my_class)
# => ["Brandi", "Zoe", "Aleksander", "Dasha", "Sonyl"]

Partner Exercise: Pop, Insert, and Append

Partner up! Choose one person to be the driver and one to be the navigator, and see if you can do the prompts:

Pop, Insert, Append Solution

1. Declare a list with the names of your classmates

my_class = [“Brandi”, “Zoe”, “Steve”, “Aleksander”, “Dasha”, “Sonyl”]

2. Print out the length of that list

print(len(my_class))

3. Print the 3rd name on the list

print(my_class[2])

4. Delete the first name on the list

deleted_classmate = my_class.pop(0)

5. Re-add the name you deleted to the end of the list

my_class.append(deleted_classmate)

print(my_class)

colors = ["red", "yellow", "green"]
print colors.append("blue")
#   => None

colors = ["red", "yellow", "green"]
colors.append("blue")
print colors
#   => ["red", "yellow", "green", "blue"]

# List Creation
my_list = ["red", 7, "yellow", 1]

# List Length
list_length = len(my_list) # 4

# List Index
print(my_list[0]) # red

# List Append
my_list.append("Yi") # ["red", 7, "yellow", 1, "Yi"]

# List Insert at Index
my_list.insert(1, "Sanju") # ["red", "Sanju", 7, "yellow", 1, "Yi"]

# List Delete
student_that_left = my_list.pop() # "Yi"; ["red", "Sanju", 7, "yellow", 1]

# List Delete at Index
student_that_left = my_list.pop(2) # 7; ["red", "Sanju", "yellow", 1]

# sum(your_numeric_list)

team_batting_avgs = [.328, .299, .208, .301, .275, .226, .253, .232, .287]
sum_avgs = sum(team_batting_avgs)
print("The total of all the batting averages is", sum_avgs)
# => 2.409

# max(your_numeric_list)
# min(your_numeric_list)

team_batting_avgs = [.328, .299, .208, .301, .275, .226, .253, .232, .287]
print("The highest batting average is", max(team_batting_avgs))
# => 0.328
print("The lowest batting average is", min(team_batting_avgs))
# => 0.208

# List Creation
my_list = ["red", 7, "yellow", 1]
# List Length
list_length = len(my_list) # 4
# List Index
print(my_list[0]) # red
# List Append
my_list.append("Yi") # ["red", 7, "yellow", 1, "Yi"]
# List Insert at Index
my_list.insert(1, "Sanju") # ["red", "Sanju", 7, "yellow", 1, "Yi"]
# List Delete
student_that_left = my_list.pop() # "Yi"; ["red", "Sanju", 7, "yellow", 1]
# List Delete at Index
student_that_left = my_list.pop(2) # 7; ["red", "Sanju", "yellow", 1]

# Sum all numbers in list
sum_avgs = sum(team_batting_avgs)
# Find minimum value of list
min(team_batting_avgs)
# Find maximum value of list
max(team_batting_avgs)