Lists

Introduction to Python for Developers

Jasmin Ludolf

Senior Data Science Content Developer

Problem

# Variables of ingredient names
ingredient_one = "pasta"
ingredient_two = "tomatoes"
ingredient_three = "garlic"
ingredient_four = "basil"
ingredient_five = "olive oil"
ingredient_six = "salt"

Lists to the rescue!

List = store multiple values in a single variable
- Can contain any combination of data types

# List of ingredients
ingredients = ["pasta", "tomatoes", "garlic", "basil", "olive oil", "salt"]

# List of ingredients using variables as values
ingredients = [ingredient_one, ingredient_two, ingredient_three,
               ingredient_four, ingredient_five, ingredient_six]

Checking the data type

# Check the data type of a list
print(type(ingredients))

<class 'list'>

Accessing elements of a list

# Print all values in the list variable
print(ingredients)

['pasta', 'tomatoes', 'garlic', 'basil', 'olive oil', 'salt']

Lists are ordered and indexed
- Python assigns index starting from zero for the first element

Accessing elements of a list

List = []
Access an element = a_list[index]

ingredients = ["pasta", "tomatoes",
"garlic", "basil", "olive oil", "salt"]

# Get the value at the first index
print(ingredients[0])

pasta

# Get the fourth element
print(ingredients[3])

basil

Finding the last element in a list

ingredients = ["pasta", "tomatoes", "garlic", "basil", "olive oil", "salt"]

# Get the last element of a list
print(ingredients[5])

salt

# Get the last element of a list
print(ingredients[-1])

salt

Accessing multiple elements

ingredients = ["pasta", "tomatoes", "garlic", "basil", "olive oil", "salt"]

# Access the second and third elements
print(ingredients[1:3])

["tomatoes", "garlic"]

[first_element:last_element + 1]
Add one to the last element's index because:
- Python returns everything up to but not including that index

Accessing multiple elements

ingredients = ["pasta", "tomatoes", "garlic", "basil", "olive oil", "salt"]

# Access all elements from the third index onwards
print(ingredients[3:])

['basil', 'olive oil', 'salt']

# Get the first three elements
print(ingredients[:3])

['pasta', 'tomatoes', 'garlic']

Alternating access

ingredients = ["pasta", "tomatoes", "garlic", "basil", "olive oil", "salt"]

# Access every second element
print(ingredients[::2])

['pasta', 'garlic', 'olive oil']]

Returns items at indexes zero, two, and four

# Access every third element, starting at the second
print(ingredients[1::3])

['tomatoes', 'olive oil']

Returns items at indexes one and four

Let's practice!

Introduction to Python for Developers