Here is a clear, complete, and exam-friendly explanation of Lists in Python, perfect for BCA/MCA/B.Tech students.

---

Lists in Python

A list in Python is an ordered, mutable (changeable) collection of items.
Lists can store different types of data such as integers, strings, floats, or even other lists.

Lists are one of the most powerful and commonly used data types in Python.

---

1. Creating a List

Lists are created using square brackets [ ].

Examples:

numbers = [10, 20, 30, 40]
fruits = ["apple", "banana", "mango"]
mixed = [10, "Python", 3.14, True]
nested = [1, 2, [3, 4], 5]   # List inside list

---

2. Accessing List Elements

Use indexing.

Python uses zero-based indexing.

Example:

fruits = ["apple", "banana", "mango"]
print(fruits[0])  # apple
print(fruits[1])  # banana
print(fruits[2])  # mango

Negative indexing:

print(fruits[-1])  # mango
print(fruits[-2])  # banana

---

3. List Slicing

Used to access a range of elements.

Syntax:

list[start : end : step]

Examples:

nums = [1, 2, 3, 4, 5, 6]

print(nums[1:4])     # [2, 3, 4]
print(nums[:3])      # [1, 2, 3]
print(nums[3:])      # [4, 5, 6]
print(nums[::2])     # [1, 3, 5]

---

4. Modifying Lists (Mutable)

Lists are mutable, meaning their elements can be changed.

Changing a value:

nums = [1, 2, 3]
nums[1] = 20
print(nums)   # [1, 20, 3]

Adding elements:

Using append():

nums.append(4)

Using insert():

nums.insert(1, 15)

---

5. Removing Elements

remove(value) – removes first occurrence

nums.remove(20)

pop(index) – removes and returns item

nums.pop(1)

del – delete by index or entire list

del nums[0]

---

6. List Methods

Python provides many useful list methods.

Method	Description
append(x)	Add element at end
extend(iterable)	Add multiple elements
insert(i, x)	Insert at index
remove(x)	Remove item
pop(i)	Remove and return item
clear()	Remove all elements
sort()	Sort list
reverse()	Reverse list
index(x)	Return index of item
count(x)	Count occurrences

---

7. Using Lists in Loops

Example:

fruits = ["apple", "banana", "mango"]
for f in fruits:
    print(f)

---

8. List Length

Use len():

len([10, 20, 30])   # 3

---

9. List Comprehension

A simple and elegant way to create lists.

Example:

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

Output:

[1, 4, 9, 16, 25]

---

10. Nested Lists

List inside another list.

matrix = [
    [1, 2],
    [3, 4],
    [5, 6]
]
print(matrix[1][0])   # 3

---

11. Checking Membership

fruits = ["apple", "banana"]
print("apple" in fruits)      # True
print("orange" not in fruits) # True

---

12. Copying Lists

Shallow copy:

new_list = old_list.copy()

Using slicing:

new_list = old_list[:]

---

13. Joining Lists

Using +:

a = [1, 2]
b = [3, 4]
c = a + b

Using extend():

a.extend(b)

---

14. Important Points About Lists

• Lists can grow dynamically.
• They are ordered.
• They allow duplicate values.
• They are mutable.
• They can contain mixed data types.

---

15. Examples for Practice

Example 1: Largest number in list

nums = [10, 5, 20, 3]
print(max(nums))

Example 2: Sum of list

print(sum(nums))

Example 3: Remove all even numbers

nums = [1, 2, 3, 4, 5, 6]
odd = [x for x in nums if x % 2 != 0]
print(odd)

---

Summary Table: Lists in Python

Feature	Description
Type	Sequence
Mutable	Yes
Ordered	Yes
Allows duplicates	Yes
Syntax	[ ]
Access	Indexing & slicing

---