List Operations
1. Creating a List
Lists are created using square brackets [], with items separated by commas.
Syntax:
my_list = [item1, item2, item3, ...]
Example:
fruits = ["apple", "banana", "cherry"]
print(fruits)
Output:
['apple', 'banana', 'cherry']
Real-world Example:
Dodagatta Nihar creates a list of his favorite books:
favorite_books = ["The Alchemist", "1984", "To Kill a Mockingbird"]
print(favorite_books)
Output:
['The Alchemist', '1984', 'To Kill a Mockingbird']
2. Accessing List Items
You can access list items by their index, with the index starting from 0.
Syntax:
item = my_list[index]
Example:
fruits = ["apple", "banana", "cherry"]
print(fruits[1])
Output:
banana
Real-world Example:
Harsha accesses his second favorite movie from a list:
favorite_movies = ["Inception", "The Matrix", "Interstellar"]
print(favorite_movies[1])
Output:
The Matrix
3. Modifying List Items
Lists are mutable, so you can change items by accessing them with their index.
Syntax:
my_list[index] = new_value
Example:
fruits = ["apple", "banana", "cherry"]
fruits[1] = "blueberry"
print(fruits)
Output:
['apple', 'blueberry', 'cherry']
Real-world Example:
Vasanta Kumar updates his list of top 3 destinations:
top_destinations = ["Paris", "London", "New York"]
top_destinations[2] = "Tokyo"
print(top_destinations)
Output:
['Paris', 'London', 'Tokyo']
4. Adding Items to a List
You can add items using the append(), extend(), and insert() methods.
Using append():
Adds an item to the end of the list.
fruits = ["apple", "banana"]
fruits.append("cherry")
print(fruits)
Output:
['apple', 'banana', 'cherry']
Using extend():
Adds all items from another list to the end of the current list.
fruits = ["apple", "banana"]
more_fruits = ["cherry", "date"]
fruits.extend(more_fruits)
print(fruits)
Output:
['apple', 'banana', 'cherry', 'date']
Using insert():
Inserts an item at a specified index.
fruits = ["apple", "banana"]
fruits.insert(1, "blueberry")
print(fruits)
Output:
['apple', 'blueberry', 'banana']
Real-world Example:
Praveen adds more tasks to his to-do list:
tasks = ["Complete assignment", "Read a book"]
tasks.append("Go for a walk")
print(tasks)
Output:
['Complete assignment', 'Read a book', 'Go for a walk']
5. Removing Items from a List
You can remove items using the remove(), pop(), and del methods.
Using remove():
Removes the first occurrence of a specified value.
fruits = ["apple", "banana", "cherry"]
fruits.remove("banana")
print(fruits)
Output:
['apple', 'cherry']
Using pop():
Removes and returns the item at a specified index. If no index is provided, it removes the last item.
fruits = ["apple", "banana", "cherry"]
removed_item = fruits.pop(1)
print(fruits)
print(f"Removed item: {removed_item}")
Output:
['apple', 'cherry']
Removed item: banana
Using del:
Deletes an item at a specified index or the entire list.
fruits = ["apple", "banana", "cherry"]
del fruits[1]
print(fruits)
Output:
['apple', 'cherry']
Real-world Example:
Dodagatta Nihar removes a book from his reading list:
reading_list = ["Book A", "Book B", "Book C"]
reading_list.remove("Book B")
print(reading_list)
Output:
['Book A', 'Book C']
6. Looping Through a List
You can loop through a list using a for loop to access each item.
Example:
fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
print(fruit)
Output:
apple
banana
cherry
Real-world Example:
Harsha prints out each item on his shopping list:
shopping_list = ["milk", "bread", "eggs"]
for item in shopping_list:
print(f"Harsha needs to buy: {item}")
Output:
Harsha needs to buy: milk
Harsha needs to buy: bread
Harsha needs to buy: eggs
7. List Slicing
List slicing allows you to extract a portion of a list.
Syntax:
sub_list = my_list[start:end]
Example:
fruits = ["apple", "banana", "cherry", "date"]
sliced_fruits = fruits[1:3]
print(sliced_fruits)
Output:
['banana', 'cherry']
Real-world Example:
Vasanta Kumar views a subset of his favorite movies:
favorite_movies = ["Movie A", "Movie B", "Movie C", "Movie D"]
selected_movies = favorite_movies[1:3]
print(selected_movies)
Output:
['Movie B', 'Movie C']
8. List Comprehensions
List comprehensions provide a concise way to create lists. They consist of an expression followed by a for clause and zero or more if clauses.
Syntax:
new_list = [expression for item in iterable if condition]
Example:
squares = [x**2 for x in range(10)]
print(squares)
Output:
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
Real-world Example:
Harsha creates a list of squares for numbers from 1 to 5:
squares = [x**2 for x in range(1, 6)]
print(squares)
Output:
[1, 4, 9, 16, 25]
Few more examples
Example 1: Creating and Modifying a List
colors = ["red", "green", "blue"]
colors.append("yellow")
colors[1] = "purple"
print(colors)
Output:
['red', 'purple', 'blue', 'yellow']
Example 2: Removing and Looping Through a List
fruits = ["apple", "banana", "cherry"]
fruits.remove("banana")
for fruit in fruits:
print(fruit)
Output:
apple
cherry
Example 3: Using List Comprehension
numbers = [1, 2, 3, 4, 5]
doubled_numbers = [x * 2 for x in numbers]
print(doubled_numbers)
Output:
[2, 4, 6, 8, 10]