Topic 12: What is List in python?

Data Type "List" in Python

In Python, a List is one of the most commonly used and versatile data types. It allows us to store multiple items in a single variable. Lists are ordered, mutable (changeable), and allow duplicate values  making them perfect for storing collections of data such as numbers, strings, or even other lists.

A List in Python is defined as a sequence of items enclosed in square brackets [ ], separated by commas.

Syntax:

list_name = [item1, item2, item3, ...]

Example:

fruits = ["apple", "banana", "cherry"]
numbers = [10, 20, 30, 40, 50]
mixed = [10, "hello", 3.14, True]

Characteristics of Python Lists

Property	Description
Ordered	The items have a defined order and can be accessed using an index.
Mutable	You can change, add, or remove items after creation.
Heterogeneous	A list can store elements of different data types.
Allows Duplicates	Lists can contain repeated elements.
Dynamic	You can add or remove elements at runtime.

Accessing Elements in a List

You can access elements using index numbers.
Python uses zero-based indexing, meaning the first element has index 0.

Syntax:

list_name[index]

Example:

fruits = ["apple", "banana", "cherry", "orange"]
print(fruits[0])   # Output: apple
print(fruits[2])   # Output: cherry

Negative Indexing:
You can also access elements from the end using negative indexes.

print(fruits[-1])  # Output: orange
print(fruits[-2])  # Output: cherry

Modifying List Elements

Lists are mutable, so you can change items after creation.

Syntax:

list_name[index] = new_value

Example:

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

Adding Elements to a List

Method	Description	Example
append()	Adds a single element to the end	fruits.append("orange")
insert()	Adds an element at a specific index	fruits.insert(1, "grapes")
extend()	Adds multiple elements (from another list)	fruits.extend(["kiwi", "melon"])

Example:

fruits = ["apple", "banana"]
fruits.append("cherry")
fruits.insert(1, "mango")
fruits.extend(["orange", "kiwi"])
print(fruits)
# Output: ['apple', 'mango', 'banana', 'cherry', 'orange', 'kiwi']

 Removing Elements from a List

Method	Description	Example
remove(value)	Removes first occurrence of a value	fruits.remove("banana")
pop(index)	Removes element at a specific index	fruits.pop(2)
clear()	Removes all elements	fruits.clear()

Example:

fruits = ["apple", "banana", "cherry"]
fruits.remove("banana")
print(fruits)     # Output: ['apple', 'cherry']

fruits.pop(0)
print(fruits)     # Output: ['cherry']

fruits.clear()
print(fruits)     # Output: []

List Operations

Python supports several operations with lists.

Operator	Description	Example
+	Concatenation	[1,2] + [3,4] → [1,2,3,4]
*	Repetition	[1,2] * 3 → [1,2,1,2,1,2]
in	Membership Test	"apple" in fruits → True
len()	Length of List	len(fruits)
max()	Maximum Value	max(numbers)
min()	Minimum Value	min(numbers)

Looping Through a List

You can iterate through list elements using a for loop.

Example:

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

Output:

apple
banana
cherry

List Slicing

Slicing allows you to access a range of elements from a list.

Syntax:

list_name[start:end]

Example:

numbers = [10, 20, 30, 40, 50, 60]
print(numbers[1:4])     # Output: [20, 30, 40]
print(numbers[:3])      # Output: [10, 20, 30]
print(numbers[3:])      # Output: [40, 50, 60]

Useful Built-in List Functions

Function	Description	Example
len(list)	Returns number of items	len(fruits)
sum(list)	Returns sum of numeric elements	sum(numbers)
sorted(list)	Returns a sorted copy	sorted(numbers)
list.count(x)	Counts occurrences of element	numbers.count(10)
list.index(x)	Returns index of element	numbers.index(20)
list.reverse()	Reverses the list	numbers.reverse()
list.sort()	Sorts the list in ascending order	numbers.sort()

Visual Representation of List Indexing

List:     [10, 20, 30, 40, 50]
Index:     0   1   2   3   4
Neg. Idx: -5  -4  -3  -2  -1

Example Program: Working with Lists

# Python program to demonstrate list operations

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

print("Original List:", numbers)

# Adding elements
numbers.append(60)
numbers.insert(2, 25)
print("After adding:", numbers)

# Removing elements
numbers.remove(40)
numbers.pop(0)
print("After removing:", numbers)

# Accessing and slicing
print("First element:", numbers[0])
print("Sublist:", numbers[1:4])

# Sorting
numbers.sort()
print("Sorted List:", numbers)

Summary

• List is a collection data type used to store multiple items in a single variable.
•  Lists are ordered, mutable, and can store different data types.
•  You can access, modify, add, or remove items easily.
•  Python provides powerful methods like append(), insert(), remove(), sort(), and more.
•  Lists make data organization and manipulation simpler and efficient.

Conclusion

The List data type is one of the cornerstones of Python programming. Whether you’re managing datasets, storing user inputs, or implementing algorithms  Lists are everywhere!

By mastering Python Lists, you build a strong foundation for working with complex data structures like Tuples, Sets, and Dictionaries. 

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