Lecture 3 – Python Data Structures (Lists, Tuples, Sets, Dictionaries)

Python Data Structures in Lecture 3 of the Python for Data Science course. Simple explanations of lists, tuples, sets, and dictionaries with examples, quiz, and practice questions for beginners.

What You Will Learn

By the end of this lecture you will understand:

• What lists, tuples, sets, and dictionaries are
• How to store multiple values in one variable
• How to add, update & remove items
• Real-world use-cases (Data Science perspective)
• MCQ quiz + practice tasks

1) What Are Data Structures?

Data structures help us store multiple values in one variable.

Example:

• 1 student → variable
• 100 students → data structure
• 1 product → variable
• thousands of products → data structure

So in Python, the MOST used structures are:

List
Tuple
Set
Dictionary

2) LIST (Most Common)

A list is an ordered, changeable collection.

Syntax:

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

You can change items

fruits[1] = "orange"

You can add items

fruits.append("grapes")

You can remove items

fruits.remove("apple")

Example (Real Data Science)

Store test scores:

scores = [85, 90, 72, 95]

3) TUPLE (Fixed collection)

A tuple is like a list but unchangeable.

Syntax:

colors = ("red", "blue", "green")

You cannot change:

colors[0] = "yellow"   # ❌ Error

When to use?

When you want data that should never change
Examples:

• Country names
• Days of the week
• Database IDs

4) SET (Unique items only)

A set has:

• No duplicate values
• No indexing
• Very fast searching

Syntax:

unique_numbers = {1, 2, 3, 3, 2}
print(unique_numbers)  

Output:

{1, 2, 3}

Good for Data Science when removing duplicate values from datasets.

For official Python documentation on data structures

5) DICTIONARY (Most powerful)

A dictionary stores data in key : value pairs.

Syntax:

student = {
    "name": "Ali",
    "age": 20,
    "grade": "A"
}

Access values

print(student["name"])

Change values

student["age"] = 21

Add new key

student["city"] = "Lahore"

Real Data Science Use

A row from a dataset is often a dictionary.

Lecture 2 – Variables & Data Types (Python Basics)

6) Real-World Example (Mini Data Science Case)

Suppose you have data of one customer:

customer = {
    "id": 101,
    "name": "Sara",
    "purchases": ["Laptop", "Mouse", "Keyboard"],
    "total_spent": 150000
}

You can now analyze:

print(customer["name"])
print(len(customer["purchases"]))

Which data structure allows duplicate values?

a) Set
b) Tuple
c) List
d) None

Answer: c) List

Which data structure is unchangeable?

a) List
b) Set
c) Tuple
d) Dictionary

Answer: c) Tuple

Which structure uses key-value pairs?

a) Set
b) List
c) Dictionary
d) Tuple

Answer: c) Dictionary

What will be the output?

x = {1, 2, 2, 3}
print(x)

a) [1, 2, 2, 3]
b) {1, 2, 3}
c) Error
d) {1, 2}

Answer: b) {1, 2, 3}

Next. Lecture 4 – Python Conditional Statements (if-else)

countries = ["Pakistan", "India", "China", "Japan", "Turkey"]
print(countries[2])

colors = ("red", "blue", "green", "yellow")
# colors[1] = "black"  # ❌ Error (tuples can't change)

nums = {1, 2, 2, 3, 3, 3}
print(nums)   # Output: {1, 2, 3}

product = {
    "name": "Laptop",
    "price": 120000,
    "quantity": 5
}
print(product)