LIST

🐍 List in Python

Understanding Python Lists with Examples

1. What is a List?

A List in Python is an ordered and mutable collection of elements. A list can contain numbers, strings, Boolean values, or even other lists. Lists are created using square brackets [ ].

my_list = [10, 20, 30, 40, 50] 

print(my_list)

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

2. Creating a List

numbers = [10, 20, 30, 40] 

 names = ["Rahul", "Amit", "Priya"] 

 mixed = [10, "Python", 3.14, True] empty = []

Output:
numbers → [10, 20, 30, 40]
names → ['Rahul', 'Amit', 'Priya']
mixed → [10, 'Python', 3.14, True]
empty → []

3. Important Properties of a List

Property	Description
Ordered	Elements maintain their insertion order.
Mutable	Elements can be changed after creation.
Allows duplicates	The same value can appear multiple times.
Heterogeneous	A list can contain different data types.
Indexed	Every element has a position/index.

4. List Indexing

Python uses zero-based indexing. Therefore, the first element has index 0.

 fruits = ["Apple", "Mango", "Banana", "Orange"] 

 print(fruits[0])

 print(fruits[2]) 

print(fruits[-1])

 Output:
Apple
Banana
Orange

💡 Tip: Negative indexing starts from the end. -1 represents the last element.

5. List Slicing

Slicing is used to extract a portion of a list.

numbers = [10, 20, 30, 40, 50] 

 print(numbers[1:4]) 

print(numbers[:3]) 

print(numbers[2:])

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

6. Changing List Elements

numbers = [10, 20, 30, 40] 

numbers[1] = 200 

print(numbers)

 Output:
[10, 200, 30, 40]

✅ Lists are mutable, so their elements can be modified after the list has been created.

7. Adding Elements to a List

numbers = [10, 20, 30] 

numbers.append(40) 

print(numbers)

Output:
[10, 20, 30, 40]

append() adds one element at the end of the list.

numbers = [10, 20, 30] 

numbers.insert(1, 15)

print(numbers)

 Output:
[10, 15, 20, 30]

insert(index, value) adds an element at a specific position.

8. Removing Elements

numbers = [10, 20, 30, 40]

numbers.remove(30)

print(numbers)

Output:
[10, 20, 40]

numbers = [10, 20, 30, 40]

numbers.pop() 

print(numbers)

Output:
[10, 20, 30]

9. Important List Methods

Method	Purpose
append()	Adds an element at the end.
insert()	Adds an element at a specified position.
remove()	Removes a specified value.
pop()	Removes an element using its index.
clear()	Removes all elements.
sort()	Sorts the list.
reverse()	Reverses the list.
count()	Counts occurrences of a value.
index()	Returns the index of a value.

10. Sorting a List

numbers = [50, 10, 40, 20, 30] 

numbers.sort() 

print(numbers)

 Output:
[10, 20, 30, 40, 50]

numbers.sort(reverse=True) print(numbers)

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

11. Traversing a List

 numbers = [10, 20, 30, 40, 50] 

for n in numbers:

    print(n)

 Output:
10
20
30
40
50

12. List Length

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

print(len(numbers))

 Output:
5

13. List Comprehension

List comprehension provides a short and elegant way to create a new list from an existing iterable.

squares = [x * x for x in range(1, 6)] 

 print(squares)

 Output:
[1, 4, 9, 16, 25]

14. Example: Student Marks

 marks = [75, 82, 68, 91, 88] 

 total = sum(marks) 

average = total / len(marks) 

print("Total =", total)

print("Average =", average)

 Output:
Total = 404
Average = 80.8

15. Quick Revision

✔ List is ordered
✔ List is mutable
✔ List uses [ ] brackets
✔ Index starts from 0
✔ Negative indexing is supported
✔ Duplicate values are allowed
✔ Different data types can be stored
✔ List supports slicing
✔ Lists provide many built-in methods

Python Programming Notes • BCA / Computer Science
Created for Academic Learning