Python : Lists

Lists are one of the most commonly used data structures in Python. They are versatile and can hold a collection of items, such as integers, strings, or even other lists. Lists are mutable, meaning you can change their elements after they have been created. Here's a rundown of the basics:

Creating a List

You can create a list by enclosing elements in square brackets `[ ]`, separated by commas.

my_list = [1, 2, 3, 4, 5]

Accessing Elements

You can access elements of a list using indexing. Python uses 0-based indexing, meaning the first element has an index of 0.

print(my_list[0]) # Output: 1 print(my_list[2]) # Output: 3

You can also use negative indexing to access elements from the end of the list:

print(my_list[-1]) # Output: 5 (last element) print(my_list[-2]) # Output: 4 (second to last element)

Slicing

You can also extract a sublist (slice) from a list using slicing notation, which has the form `[start:stop:step]`.

print(my_list[1:4]) # Output: [2, 3, 4] (elements from index 1 to 3) print(my_list[:3]) # Output: [1, 2, 3] (elements from start to index 2) print(my_list[2:]) # Output: [3, 4, 5] (elements from index 2 to end) print(my_list[::2]) # Output: [1, 3, 5] (every second element)

Modifying Lists

Lists are mutable, so you can change their elements after creation.

my_list[0] = 10 print(my_list) # Output: [10, 2, 3, 4, 5]

List Methods

Python provides several built-in methods to manipulate lists:

append() : Add an element to the end of the list.
extend() : Add elements from another list to the end of the list.
insert() : Insert an element at a specified position.
remove() : Remove the first occurrence of a value from the list.
pop() : Remove and return an element at a specified index (default is the last element).
index() : Return the index of the first occurrence of a value.
count() : Return the number of occurrences of a value.
sort() : Sort the list in ascending order.
reverse() : Reverse the elements of the list.

Iterating Over Lists

You can iterate over the elements of a list using a `for` loop:

for item in my_list: print(item)

Checking Membership

You can check if an element is present in a list using the `in` operator:

if 3 in my_list: print("3 is in the list")

This covers the basics of lists in Python.

Index