Lesson 26 of 70 – Python Lists

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Python Lists

A list is one of the most commonly used data structures in Python. A list is used to store multiple values in a single variable.

Lists are ordered, changeable (mutable), and allow duplicate values.

Note: Python lists are written using square brackets [ ].

What is a List?

A list is a collection of multiple items stored in a single variable.

students = ["Amit", "Rahul", "Priya"]

print(students)

Output:
['Amit', 'Rahul', 'Priya']

Creating a List

A list is created using square brackets.

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

print(numbers)

Output:
[10, 20, 30, 40, 50]

List with Different Data Types

A Python list can contain different types of values.

data = [10, "Python", 25.5, True]

print(data)

Output:
[10, 'Python', 25.5, True]

List with Duplicate Values

Lists allow duplicate values.

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

print(numbers)

Output:
[10, 20, 10, 30, 20]

List Indexing

List elements are accessed using their index. Python list indexing starts from 0.

names = ["Amit", "Rahul", "Priya"]

print(names[0])
print(names[1])
print(names[2])

Output:
Amit
Rahul
Priya

Negative Indexing

Python also supports negative indexing. The last element has index -1.

names = ["Amit", "Rahul", "Priya"]

print(names[-1])
print(names[-2])

Output:
Priya
Rahul

Changing List Items

Lists are mutable, which means their elements can be changed after the list is created.

names = ["Amit", "Rahul", "Priya"]

names[1] = "Ravi"

print(names)

Output:
['Amit', 'Ravi', 'Priya']

List Length

The len() function returns the number of elements in a list.

numbers = [10, 20, 30, 40]

print(len(numbers))

Output:
4

Checking an Item in a List

The in operator checks whether an item exists in a list.

names = ["Amit", "Rahul", "Priya"]

print("Rahul" in names)
print("Ravi" in names)

Output:
True
False

Checking an Item Not in a List

numbers = [10, 20, 30]

print(50 not in numbers)

Output:
True

List Slicing

Slicing is used to get a portion of a list.

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

print(numbers[1:4])

Output:
[20, 30, 40]

The start index is included and the stop index is excluded.

List Slicing from Beginning

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

print(numbers[:3])

Output:
[10, 20, 30]

List Slicing to End

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

print(numbers[2:])

Output:
[30, 40, 50]

Negative Slicing

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

print(numbers[-3:])

Output:
[30, 40, 50]

Loop Through a List

names = ["Amit", "Rahul", "Priya"]

for name in names:
    print(name)

Output:
Amit
Rahul
Priya

List with While Loop

numbers = [10, 20, 30]

i = 0

while i < len(numbers):
    print(numbers[i])
    i += 1

Output:
10
20
30

Nested List

A list can contain other lists. This is called a nested list.

students = [
    ["Amit", 20],
    ["Rahul", 21],
    ["Priya", 19]
]

print(students)

Output:
[['Amit', 20], ['Rahul', 21], ['Priya', 19]]

Accessing Nested List

students = [
    ["Amit", 20],
    ["Rahul", 21]
]

print(students[0][0])
print(students[1][1])

Output:
Amit
21

List Concatenation

The + operator can be used to combine two lists.

list1 = [10, 20]
list2 = [30, 40]

result = list1 + list2

print(result)

Output:
[10, 20, 30, 40]

Repeating a List

The * operator can repeat the elements of a list.

numbers = [1, 2]

print(numbers * 3)

Output:
[1, 2, 1, 2, 1, 2]

Copying a List

The copy() method can be used to create a shallow copy of a list.

numbers = [10, 20, 30]

new_numbers = numbers.copy()

print(new_numbers)

Output:
[10, 20, 30]

List Assignment vs Copy

Simply assigning one list to another does not create an independent copy.

list1 = [10, 20, 30]

list2 = list1

list2[0] = 100

print(list1)

Output:
[100, 20, 30]

Both variables refer to the same list object.

List Constructor

The list() constructor can be used to create a list from another iterable.

text = "Python"

letters = list(text)

print(letters)

Output:
['P', 'y', 't', 'h', 'o', 'n']

List Unpacking

List elements can be assigned to multiple variables.

student = ["Rahul", 20, "Python"]

name, age, course = student

print(name)
print(age)
print(course)

Output:
Rahul
20
Python

Important List Properties

Lists are ordered.
Lists are changeable.
Lists allow duplicate values.
Lists can contain different data types.
Lists support positive and negative indexing.
Lists support slicing.
Lists can contain other lists.
Lists are written using square brackets.

Key Points

A list stores multiple values in one variable.
Lists are created using square brackets [ ].
List indexing starts from 0.
Negative indexing starts from -1.
Lists are mutable.
Lists allow duplicate values.
The len() function returns the number of elements.
List elements can be changed after creation.
Lists support slicing.
Lists can contain different data types.
Lists can be nested.

🧠 Quick Quiz

Question: Which brackets are used to create a list in Python?

( )
[ ]
{ }
< >

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