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Nested Lists

A nested list in Python is a list that contains other sublists as its elements. This structure is particularly useful for grouping related items within a main list, where each sublist often shares common attributes or relationships.

To access elements within these sublists, indexing is used sequentially — meaning, we select the main list index first and then the sublist index. The following practical application and diagram provide a detailed look at how you can create and manage nested lists effectively.

Example Application

A customer in your grocery store has compiled a list of grocery items, where each item's details are stored in sublists under variable names.

We will help the customer access details from the milk sublist, add a new item, remove an existing item, and sort the entire grocery_list.

Let's start by creating a list first, and go step by step:


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# Define individual grocery items as lists containing details
bread = ["Bread", 4.80, 3, "Gluten Free"] # Item name, price, quantity, type
milk = ["Milk", 5.99, 2, "2% Milk"]   # Item name, price, quantity, type
apple = ["Apple", 1.27, 12, "Fuji"] # Item name, price, quantity, type

# Create the main grocery list that contains these items
grocery_list = [bread, apple, milk]
print("Grocery List:" , grocery_list)

# Accessing and printing specific item details using indexing
print("Item:", grocery_list[2][0]) # Accesses "Milk" title
print("Price:", grocery_list[2][1]) # Accesses price of a Milk, which is 5.99
print("Quantity:", grocery_list[2][2]) # Accesses quantity of Milk, which is 2
print("Type:", grocery_list[2][3]) # Accesses type of Milk, which is "2% Milk"

# Adding a new sublist item to the grocery list
onion = ["Onions", 1.30, 10, "Yellow"]
grocery_list.append(onion)

# Removing an item from the grocery list
grocery_list.remove(bread)

# Sorting the grocery list alphabetically
grocery_list.sort()
print("Updated Grocery List:", grocery_list)

The diagram below illustrates the nested list structure of grocery_list. Each item in the list, such as milk, apple, and bread, is itself a list containing a specific item details.

For instance, to access the price of milk, which is stored in the milk sublist, you use the syntax grocery_list[2][1]. Here, grocery_list[2] selects the milk sublist, and grocery_list[2][1] goes a step further to access the second element of that sublist — the price.

Task

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Update an inventory list for a grocery store's vegetable section by removing an item, adding two new items, and sorting the list alphabetically without duplicates.

Create a variable vegetables with the list ["tomatoes", "potatoes", "onions"].
Remove "onions" from the list.
Add "carrots" to the list if it’s not already there.
Add "cucumbers" to the list if it’s not already there.
Sort the list alphabetically.

Output Requirements

Print the updated vegetable list: "Updated Vegetable Inventory: <$vegetables>".
If "carrots" is already in the list, print: "Carrots are already in the list."
If "cucumbers" is already in the list, print: "Cucumbers are already in the list."

Solution

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Section 4. Chapter 2

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Nested Lists

Example Application

A customer in your grocery store has compiled a list of grocery items, where each item's details are stored in sublists under variable names.

We will help the customer access details from the milk sublist, add a new item, remove an existing item, and sort the entire grocery_list.

Let's start by creating a list first, and go step by step:


              12345678910111213141516171819202122232425
            
# Define individual grocery items as lists containing details
bread = ["Bread", 4.80, 3, "Gluten Free"] # Item name, price, quantity, type
milk = ["Milk", 5.99, 2, "2% Milk"]   # Item name, price, quantity, type
apple = ["Apple", 1.27, 12, "Fuji"] # Item name, price, quantity, type

# Create the main grocery list that contains these items
grocery_list = [bread, apple, milk]
print("Grocery List:" , grocery_list)

# Accessing and printing specific item details using indexing
print("Item:", grocery_list[2][0]) # Accesses "Milk" title
print("Price:", grocery_list[2][1]) # Accesses price of a Milk, which is 5.99
print("Quantity:", grocery_list[2][2]) # Accesses quantity of Milk, which is 2
print("Type:", grocery_list[2][3]) # Accesses type of Milk, which is "2% Milk"

# Adding a new sublist item to the grocery list
onion = ["Onions", 1.30, 10, "Yellow"]
grocery_list.append(onion)

# Removing an item from the grocery list
grocery_list.remove(bread)

# Sorting the grocery list alphabetically
grocery_list.sort()
print("Updated Grocery List:", grocery_list)

The diagram below illustrates the nested list structure of grocery_list. Each item in the list, such as milk, apple, and bread, is itself a list containing a specific item details.

Task

Swipe to start coding

Update an inventory list for a grocery store's vegetable section by removing an item, adding two new items, and sorting the list alphabetically without duplicates.

Create a variable vegetables with the list ["tomatoes", "potatoes", "onions"].
Remove "onions" from the list.
Add "carrots" to the list if it’s not already there.
Add "cucumbers" to the list if it’s not already there.
Sort the list alphabetically.

Output Requirements

Print the updated vegetable list: "Updated Vegetable Inventory: <$vegetables>".
If "carrots" is already in the list, print: "Carrots are already in the list."
If "cucumbers" is already in the list, print: "Cucumbers are already in the list."

Solution

Switch to desktop for real-world practiceContinue from where you are using one of the options below

Everything was clear?

Thanks for your feedback!

Section 4. Chapter 2

Switch to desktop for real-world practiceContinue from where you are using one of the options below