Python Lists Tutorial

 

Python Lists Tutorial

1. What is a List?

A list is a collection of items that can be of different types. Lists are ordered, mutable (changeable), and allow duplicate values.

2. Creating a List

You can create a list by placing items inside square brackets [], separated by commas.

python
1# Creating an empty list
2my_list = []
3
4# Creating a list with integers
5numbers = [1, 2, 3, 4, 5]
6
7# Creating a list with mixed data types
8mixed_list = [1, "Hello", 3.14, True]
9
10# Creating a list of lists (nested list)
11nested_list = [[1, 2, 3], ["a", "b", "c"]]

3. Accessing List Elements

You can access elements in a list using their index. Remember that Python uses zero-based indexing.

python
1# Accessing elements
2print(numbers[0])  # Output: 1
3print(mixed_list[1])  # Output: Hello
4print(nested_list[1][0])  # Output: a

4. Modifying Lists

Lists are mutable, meaning you can change their content.

python
1# Changing an element
2numbers[0] = 10
3print(numbers)  # Output: [10, 2, 3, 4, 5]
4
5# Adding elements
6numbers.append(6)  # Adds 6 to the end of the list
7print(numbers)  # Output: [10, 2, 3, 4, 5, 6]
8
9# Inserting elements
10numbers.insert(1, 15)  # Inserts 15 at index 1
11print(numbers)  # Output: [10, 15, 2, 3, 4, 5, 6]
12
13# Removing elements
14numbers.remove(15)  # Removes the first occurrence of 15
15print(numbers)  # Output: [10, 2, 3, 4, 5, 6]
16
17# Popping elements
18popped_element = numbers.pop()  # Removes and returns the last element
19print(popped_element)  # Output: 6
20print(numbers)  # Output: [10, 2, 3, 4, 5]

5. List Methods

Python provides several built-in methods to manipulate lists.

• append(): Adds an item to the end of the list.
• extend(): Adds elements from another list to the end of the current list.
• insert(): Inserts an item at a specified index.
• remove(): Removes the first occurrence of a specified value.
• pop(): Removes and returns an item at a specified index (default is the last item).
• clear(): Removes all items from the list.
• 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 list.

python
1# Using some list methods
2numbers.extend([7, 8, 9])  # Extends the list with another list
3print(numbers)  # Output: [10, 2, 3, 4, 5, 7, 8, 9]
4
5numbers.sort()  # Sorts the list
6print(numbers)  # Output: [2, 3, 4, 5, 7, 8, 10]
7
8numbers.reverse()  # Reverses the list
9print(numbers)  # Output: [10, 8, 7, 5, 4, 3, 2]

6. List Comprehensions

List comprehensions provide a concise way to create lists. They consist of brackets containing an expression followed by a for clause.

python
1# Creating a list of squares using list comprehension
2squares = [x**2 for x in range(10)]
3print(squares)  # Output: [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
4
5# Filtering with list comprehension
6even_squares = [x**2 for x in range(10) if x % 2 == 0]
7print(even_squares)  # Output: [0, 4, 16,