Modifying a List

In Python, lists are mutable, which means that after a list is created, its contents can be modified, added, or removed. Because of this mutability, lists have much flexibility for working with lists and are, therefore, a very powerful tool for managing dynamic data.

What Does "Mutable" Mean?

Mutable means that the data structure can be updated without creating a new object. For example, you could change the value of an existing item, replace several elements, or even remove and insert new ones directly into the same list.

Imagine you have a list of cities you plan to visit, but plans change. You can update or replace items in the list easily:


              123456789
            
cities = ["Paris", "Tokyo", "New York", "Berlin", "Sydney"]

# Replacing the fourth city
cities[2] = "Rome"
print(cities)  # Output: ['Paris', 'Tokyo', 'Rome', 'Berlin', 'Sydney']

# Replacing the last two cities with new ones
cities[-2:] = ["Dubai", "Cape Town"]
print(cities)  # Output: ['Paris', 'Tokyo', 'Rome', 'Dubai', 'Cape Town']

In this example:

We replaced the city "New York" at index 3 with "Rome";
Using negative indexing, we replaced the last two cities ("Rome" and "Sydney") with "Dubai" and "Cape Town".

You can also make multiple changes in one step:


              123456
            
cities = ["Paris", "Tokyo", "New York", "Berlin", "Sydney"]

# Replacing multiple cities in the middle
cities[1:3] = ["Seoul", "Bangkok", "Mumbai"]

print(cities)  # Output: ['Paris', 'Seoul', 'Bangkok', 'Mumbai', 'Berlin', 'Sydney']

Here, we replaced "Tokyo" and "New York" with three cities: "Seoul", "Bangkok", and "Mumbai". This demonstrates how flexible list mutability can be for managing your data.

Task

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Update the estimated cost of your first city to include a discount. Apply a 20% reduction to the cost.

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

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Section 1. Chapter 5

Modifying a List

What Does "Mutable" Mean?

Imagine you have a list of cities you plan to visit, but plans change. You can update or replace items in the list easily:


              123456789
            
cities = ["Paris", "Tokyo", "New York", "Berlin", "Sydney"]

# Replacing the fourth city
cities[2] = "Rome"
print(cities)  # Output: ['Paris', 'Tokyo', 'Rome', 'Berlin', 'Sydney']

# Replacing the last two cities with new ones
cities[-2:] = ["Dubai", "Cape Town"]
print(cities)  # Output: ['Paris', 'Tokyo', 'Rome', 'Dubai', 'Cape Town']

In this example:

We replaced the city "New York" at index 3 with "Rome";
Using negative indexing, we replaced the last two cities ("Rome" and "Sydney") with "Dubai" and "Cape Town".

You can also make multiple changes in one step:


              123456
            
cities = ["Paris", "Tokyo", "New York", "Berlin", "Sydney"]

# Replacing multiple cities in the middle
cities[1:3] = ["Seoul", "Bangkok", "Mumbai"]

print(cities)  # Output: ['Paris', 'Seoul', 'Bangkok', 'Mumbai', 'Berlin', 'Sydney']

Here, we replaced "Tokyo" and "New York" with three cities: "Seoul", "Bangkok", and "Mumbai". This demonstrates how flexible list mutability can be for managing your data.

Task

Swipe to show code editor

Update the estimated cost of your first city to include a discount. Apply a 20% reduction to the cost.

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 1. Chapter 5

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