Lists in Python

A List in Python is a data structure that allows you to store multiple items in a single variable. Lists are ordered, mutable, and can contain elements of different data types.

Creating a List

You create a list using square brackets []:

# Empty List
empty_list = []

# List of Integers
numbers = [1, 2, 3, 4, 5]

# List of Strings
fruits = ["apple", "banana", "cherry"]

# Mixed Data Types
mixed = [1, "hello", 3.14, True]

Indexing

Indexing means accessing elements by their position.

• Index starts from 0 in Python:

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

print(fruits[0])  # apple
print(fruits[1])  # banana
print(fruits[2])  # cherry

• Negative indexing starts from the end:

print(fruits[-1])  # cherry
print(fruits[-2])  # banana
print(fruits[-3])  # apple

Slicing

Slicing lets you extract a sublist:

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

print(numbers[1:4])    # [20, 30, 40]
print(numbers[:3])     # [10, 20, 30]
print(numbers[2:])     # [30, 40, 50]
print(numbers[-3:-1])  # [30, 40]

Syntax:

list[start:stop:step]

Example with step:

print(numbers[::2])  # [10, 30, 50]

Modifying Elements

Lists are mutable, which means you can change their contents:

fruits = ["apple", "banana", "cherry"]
fruits[1] = "mango"
print(fruits)  # ['apple', 'mango', 'cherry']

List Methods

Python provides many built-in methods for lists:

Method	Description
append(x)	Adds an item to the end of the list
insert(i, x)	Inserts an item at a specific index
extend(iter)	Adds all elements from another iterable
remove(x)	Removes the first occurrence of the item
pop([i])	Removes and returns the item at the given index
clear()	Removes all elements
index(x)	Returns the index of the first occurrence of the item
count(x)	Counts how many times the item appears
sort()	Sorts the list in ascending order
reverse()	Reverses the list
copy()	Returns a shallow copy of the list

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Examples

append()

nums = [1, 2, 3]
nums.append(4)
print(nums)  # [1, 2, 3, 4]

insert()

nums.insert(1, 100)
print(nums)  # [1, 100, 2, 3, 4]

extend()

nums.extend([5, 6])
print(nums)  # [1, 100, 2, 3, 4, 5, 6]

remove() and pop()

nums.remove(100)
print(nums)  # [1, 2, 3, 4, 5, 6]

nums.pop()   # Removes the last element
print(nums)  # [1, 2, 3, 4, 5]

nums.pop(2)  # Removes index 2
print(nums)  # [1, 2, 4, 5]

Iterating Through a List

Using a for loop:

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

for item in fruits:
    print(item)

Output:

apple
banana
cherry

Using indices:

for i in range(len(fruits)):
    print(i, fruits[i])

Membership Test

Check whether an item exists in the list:

print("apple" in fruits)       # True
print("mango" not in fruits)   # True

Nested Lists

Lists can contain other lists:

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

print(matrix[0])       # [1, 2, 3]
print(matrix[1][2])    # 6

List Comprehensions

A concise way to create new lists:

squares = [x**2 for x in range(1, 6)]
print(squares)  # [1, 4, 9, 16, 25]

With a condition:

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

Copying Lists

Be careful! Assigning directly creates a reference:

a = [1, 2, 3]
b = a
b.append(4)

print(a)  # [1, 2, 3, 4]

To create an independent copy:

c = a.copy()
c.append(5)

print(a)  # [1, 2, 3, 4]
print(c)  # [1, 2, 3, 4, 5]

Conclusion

Python Lists are a powerful and flexible data structure used everywhere—from collecting and processing data to building complex programs. Practice using list methods and experiment to become confident.