Python Lists

What is a List?

A list in Python is a versatile data structure that represents an ordered collection of items. It's mutable, meaning you can change its contents after it's created. Lists are defined by enclosing elements within square brackets [] and separated by commas.

Creating a List

Python

my_list = [1, 2, 3, "apple", True]

As you can see, lists can contain items of different data types.

Accessing List Elements

You can access individual elements using their index. Indexing starts from 0.

Python

my_list = [10, 20, 30, 40]

first_element = my_list[0]  # Accesses the first element (10)

third_element = my_list[2]  # Accesses the third element (30)

Slicing Lists

You can extract a portion of a list using slicing:

Python

my_list = [10, 20, 30, 40, 50]

sublist = my_list[1:4]  # Extracts elements from index 1 to 3 (inclusive)

print(sublist)  # Output: [20, 30, 40]

Modifying Lists

Lists are mutable, meaning you can change their contents.

Python

my_list = [10, 20, 30]

my_list[1] = 25  # Change the second element

my_list.append(40)  # Add an element to the end

my_list.insert(1, 15)  # Insert an element at index 1

my_list.remove(20)  # Remove the first occurrence of 20

del my_list[0]  # Delete the element at index 0

List Methods

Python provides several built-in methods for manipulating lists:

• append(): Adds an element to the end of the list.

• extend(): Appends the elements of another list to the end of the current list.

• insert(): Inserts an element at a specific index.

• remove(): Removes the first occurrence of a specified value.

• pop(): Removes and returns the element at a specific index (or the last element if no index is specified).

• index(): Returns the index of the first occurrence of a specified value.

• count(): Returns the number of occurrences of a specified value.

• sort(): Sorts the list in ascending order.

• reverse(): Reverses the order of the elements in the list.

• clear(): Removes all elements from the list.

Example

Python

my_list = [3, 1, 4, 1, 5, 9]

my_list.sort()

print(my_list)  # Output: [1, 1, 3, 4, 5, 9]

my_list.reverse()

print(my_list)  # Output: [9, 5, 4, 3, 1, 1]

Important Points

• Lists can contain any data type, including other lists.

• Lists are dynamic, meaning their size can change as elements are added or removed.

• Lists are mutable, so changes made to a list affect the original list.

By understanding these concepts and methods, you can effectively use lists in your Python programs to store and manipulate data.