Introduction to Lists in Python

What is a List?

A list in Python is a collection of ordered, mutable, and heterogeneous elements. This means:

• Ordered ? Items have a fixed sequence.
• Mutable ? You can change, add, or remove elements.
• Heterogeneous ? A list can contain different data types (strings, numbers, booleans, even other lists!).

Lists are one of Python’s most powerful and flexible data structures. They allow you to store multiple values in a single variable.

Creating a List

To create a list, use square brackets [ ], separating elements with commas.

# Example of a list
fruits = ["apple", "banana", "cherry"]
numbers = [10, 20, 30, 40]
mixed = [1, "hello", True, 3.5]

Accessing Elements in a List

You can access list items using indexing. In Python, indexing starts from 0.

fruits = ["apple", "banana", "cherry"]

print(fruits[0])  # Output: apple
print(fruits[1])  # Output: banana
print(fruits[2])  # Output: cherry

Negative Indexing

You can also use negative indexes to access elements from the end of the list.

print(fruits[-1])  # Output: cherry
print(fruits[-2])  # Output: banana

Modifying a List

Since lists are mutable, we can modify elements using their index.

fruits = ["apple", "banana", "cherry"]
fruits[1] = "orange"

print(fruits)  # Output: ['apple', 'orange', 'cherry']

List Length

To find the number of items in a list, use the len() function.

print(len(fruits))  # Output: 3

Checking if an Item Exists in a List

Use the in keyword to check for the presence of an item.

print("banana" in fruits)  # Output: False
print("orange" in fruits)  # Output: True

Exercise: Try It Yourself!

1. Create a list of your favorite movies.
2. Print the first and last movie from the list using both positive and negative indexing.
3. Modify the second item in the list.
4. Check if a specific movie is in the list.