List

Python lists are a versatile and commonly used data structure that can hold an ordered collection of items (of any data type)

1. Creating a List

A list is created by placing items inside square brackets [], separated by commas.

# Empty list
empty_list = []

# List with integers
numbers = [1, 2, 3, 4, 5]

# List with strings
fruits = ["apple", "banana", "cherry"]

# Mixed data types
mixed = [1, "hello", 3.14, True]

# Nested list
nested = [[1, 2], [3, 4], [5, 6]]

2. Accessing List Elements

• Use indexing to access elements (starting at 0).
• Use negative indexing for elements from the end (-1).

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

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

3. Modifying a List

Lists are mutable, so you can change elements.

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

# Change an item
fruits[1] = "blueberry"
print(fruits)  # Output: ['apple', 'blueberry', 'cherry']

# Add a new item (append)
fruits.append("date")
print(fruits)  # Output: ['apple', 'blueberry', 'cherry', 'date']

# Insert at a specific index
fruits.insert(1, "mango")
print(fruits)  # Output: ['apple', 'mango', 'blueberry', 'cherry', 'date']

4. Removing Elements

Use remove(), pop(), or del to remove elements.

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

# Remove by value
fruits.remove("banana")
print(fruits)  # Output: ['apple', 'cherry', 'date']

# Remove by index
fruits.pop(1)
print(fruits)  # Output: ['apple', 'date']

# Remove the last item
fruits.pop()
print(fruits)  # Output: ['apple']

# Delete a specific index
del fruits[0]
print(fruits)  # Output: []

# Clear the list
fruits = ["apple", "banana", "cherry"]
fruits.clear()
print(fruits)  # Output: []

5. Iterating Through a List

You can loop through a list using a for loop.

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

for fruit in fruits:
    print(fruit) # Prints only value


for i, fruit in enumerate(fruits):
    print(i, fruit) # Prints with index

6. List Operations

list1 = [1, 2]
list2 = [3, 4]
combined = list1 + list2
print(combined)  # Output: [1, 2, 3, 4]

list1 = [1, 2]
print(list1 * 3)  # Output: [1, 2, 1, 2, 1, 2]

fruits = ["apple", "banana", "cherry"]
print("apple" in fruits)  # Output: True
print("date" in fruits)   # Output: False

7. Slicing Lists

Retrieve a subset of elements using slicing.

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

print(fruits[1:3])  # Output: ['banana', 'cherry']
print(fruits[:2])   # Output: ['apple', 'banana']
print(fruits[2:])   # Output: ['cherry', 'date']
print(fruits[-2:])  # Output: ['cherry', 'date']

8. List Methods

List Methods in Python

Method	Description
append(x)	Adds an element to the end of the list.
extend(iterable)	Adds all elements of an iterable to the end of the list.
insert(i, x)	Inserts an element at a specific position.
remove(x)	Removes the first occurrence of the element.
pop([i])	Removes and returns an element by index (default last).
clear()	Removes all elements from the list.
index(x)	Returns the index of the first occurrence of the element.
count(x)	Returns the number of occurrences of the element.
sort()	Sorts the list in ascending order (or with a key).
reverse()	Reverses the list in place.
copy()	Returns a shallow copy of the list.

9. List Comprehension

# Squares of numbers
squares = [x ** 2 for x in range(5)]
print(squares)  # Output: [0, 1, 4, 9, 16]

# Filter even numbers
evens = [x for x in range(10) if x % 2 == 0]
print(evens)  # Output: [0, 2, 4, 6, 8]

10. Nested Lists

matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

print(matrix[1][2])  # Output: 6

for row in matrix:
    for item in row:
        print(item, end=" ")