Python Collections from Level 0

0. What is a Collection?

A collection is a way to store many values inside one variable.

Without collections, we may write:

Without collection

student1 = "Amit"
student2 = "Riya"
student3 = "Karan"

print(student1)
print(student2)
print(student3)

With a collection, we can write:

With collection

students = ["Amit", "Riya", "Karan"]

print(students)

Simple meaning: A collection is a container for many values.

List Ordered and changeable collection.

Tuple Ordered but not changeable collection.

Set Unique values only. Duplicate values are removed.

Frozenset A set that cannot be changed.

Dictionary Stores data as key-value pairs.

1. List

A list is an ordered collection of values. Lists are written using square brackets: [].

Basic list

marks = [80, 75, 90]

Features of List

Ordered
Changeable
Allows duplicate values
Uses square brackets: []

List Example 1: Student Names

Python code

students = ["Amit", "Riya", "Karan"]

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

Output

['Amit', 'Riya', 'Karan']
Amit
Riya
Karan

Python indexing starts from 0. So students[0] means the first item.

List Example 2: Add and Change Values

Python code

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

print("Original list:", fruits)

fruits.append("orange")
print("After adding orange:", fruits)

fruits[1] = "grapes"
print("After changing banana to grapes:", fruits)

Output

Original list: ['apple', 'banana', 'mango']
After adding orange: ['apple', 'banana', 'mango', 'orange']
After changing banana to grapes: ['apple', 'grapes', 'mango', 'orange']

2. Tuple

A tuple is also an ordered collection. Tuples are written using round brackets: ().

Basic tuple

point = (10, 20)

Features of Tuple

Ordered
Not changeable
Allows duplicate values
Uses round brackets: ()

Main difference: list can be changed, but tuple cannot be changed.

Tuple Example 1: Coordinates

Python code

point = (10, 20)

print(point)
print("x =", point[0])
print("y =", point[1])

Output

(10, 20)
x = 10
y = 20

Tuple Example 2: Days of Week

Python code

days = ("Monday", "Tuesday", "Wednesday", "Thursday", "Friday")

print(days)
print(days[0])
print(days[4])

Output

('Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday')
Monday
Friday

What happens if we try to change a tuple?

This gives an error

days = ("Monday", "Tuesday", "Wednesday")

days[0] = "Sunday"

Error

TypeError: 'tuple' object does not support item assignment

3. Set

A set is a collection of unique values. Sets are written using curly brackets: {}.

Basic set

numbers = {1, 2, 3}

Features of Set

Unordered
Changeable
Does not allow duplicate values
Uses curly brackets: {}

Set Example 1: Remove Duplicates Automatically

Python code

numbers = {1, 2, 3, 2, 1, 4}

print(numbers)

Output may be

{1, 2, 3, 4}

A set keeps only unique values. Duplicate values are removed automatically.

Set Example 2: Add and Remove Items

Python code

subjects = {"Python", "Java", "SQL"}

print("Original set:", subjects)

subjects.add("HTML")
print("After adding HTML:", subjects)

subjects.remove("Java")
print("After removing Java:", subjects)

Output may be

Original set: {'Python', 'Java', 'SQL'}
After adding HTML: {'Python', 'Java', 'SQL', 'HTML'}
After removing Java: {'Python', 'SQL', 'HTML'}

The output order may be different because sets are unordered.

4. Frozenset

A frozenset is like a set, but it cannot be changed.

Basic frozenset

numbers = frozenset([1, 2, 3])

Features of Frozenset

Unordered
Not changeable
Does not allow duplicate values
Created using frozenset()

Think of a frozenset as a frozen set. It is locked after creation.

Frozenset Example 1: Create a Frozenset

Python code

numbers = frozenset([1, 2, 3, 2, 1])

print(numbers)

Output

frozenset({1, 2, 3})

Frozenset Example 2: Check Membership

Python code

subjects = frozenset(["Python", "Java", "SQL"])

print("Python" in subjects)
print("HTML" in subjects)

Output

True
False

What happens if we try to add to a frozenset?

This gives an error

subjects = frozenset(["Python", "Java", "SQL"])

subjects.add("HTML")

Error

AttributeError: 'frozenset' object has no attribute 'add'

5. Dictionary

A dictionary stores data in key-value pairs.

Basic dictionary

student = {
    "name": "Amit",
    "age": 15,
    "marks": 88
}

Each item has a key and a value:

Key-value pair

"name": "Amit"

"name" is the key
"Amit" is the value

Features of Dictionary

Ordered
Changeable
Does not allow duplicate keys
Stores key-value pairs

Dictionary Example 1: Student Data

Python code

student = {
    "name": "Amit",
    "age": 15,
    "marks": 88
}

print(student)
print(student["name"])
print(student["age"])
print(student["marks"])

Output

{'name': 'Amit', 'age': 15, 'marks': 88}
Amit
15
88

Dictionary Example 2: Add and Update Values

Python code

student = {
    "name": "Riya",
    "age": 14,
    "marks": 91
}

print("Original dictionary:", student)

student["city"] = "Varanasi"
print("After adding city:", student)

student["marks"] = 95
print("After updating marks:", student)

Output

Original dictionary: {'name': 'Riya', 'age': 14, 'marks': 91}
After adding city: {'name': 'Riya', 'age': 14, 'marks': 91, 'city': 'Varanasi'}
After updating marks: {'name': 'Riya', 'age': 14, 'marks': 95, 'city': 'Varanasi'}

Comparison Table

Collection	Brackets / Syntax	Ordered	Changeable	Allows Duplicates	Example
List	`[]`	Yes	Yes	Yes	`[1, 2, 2, 3]`
Tuple	`()`	Yes	No	Yes	`(1, 2, 2, 3)`
Set	`{}`	No	Yes	No	`{1, 2, 3}`
Frozenset	`frozenset()`	No	No	No	`frozenset([1, 2, 3])`
Dictionary	`{key: value}`	Yes	Yes	Keys cannot repeat	`{"name": "Amit"}`

One Program Using All Collections

Python code

# List
students = ["Amit", "Riya", "Karan"]

# Tuple
days = ("Monday", "Tuesday", "Wednesday")

# Set
unique_marks = {80, 90, 80, 75, 90}

# Frozenset
fixed_subjects = frozenset(["Python", "Maths", "English"])

# Dictionary
student_details = {
    "name": "Amit",
    "age": 15,
    "marks": 88
}

print("List:", students)
print("Tuple:", days)
print("Set:", unique_marks)
print("Frozenset:", fixed_subjects)
print("Dictionary:", student_details)

Output may be

List: ['Amit', 'Riya', 'Karan']
Tuple: ('Monday', 'Tuesday', 'Wednesday')
Set: {80, 90, 75}
Frozenset: frozenset({'Python', 'Maths', 'English'})
Dictionary: {'name': 'Amit', 'age': 15, 'marks': 88}

When Should We Use What?

Use List When you want many values, want order, and want to change the values later.

shopping_list = ["rice", "dal", "milk"]

Use Tuple When you want fixed values that should not change.

rgb_color = (255, 0, 0)

Use Set When you want unique values only.

roll_numbers = {1, 2, 3, 4}

Use Frozenset When you want unique values that should not change.

allowed_subjects = frozenset(["Python", "Java", "SQL"])

Use Dictionary When you want to store meaningful records with names.

student = {
    "name": "Amit",
    "class": 9,
    "city": "Varanasi"
}

Practice Questions

Question 1

Create a list of 5 fruits and print the second fruit.

Solution

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

print(fruits[1])

Question 2

Create a tuple of 3 numbers and print the last number.

Solution

numbers = (10, 20, 30)

print(numbers[2])

Question 3

Create a set with duplicate numbers and print it.

Solution

numbers = {1, 2, 2, 3, 3, 4}

print(numbers)

Question 4

Create a frozenset of subjects and check whether "Python" is present.

Solution

subjects = frozenset(["Python", "Java", "SQL"])

print("Python" in subjects)

Question 5

Create a dictionary for a student with name, age, and marks.

Solution

student = {
    "name": "Riya",
    "age": 14,
    "marks": 92
}

print(student)
print(student["name"])
print(student["marks"])

Mini Project: Student Record System

This mini project combines list, dictionary, set, and tuple.

Python code

students = [
    {
        "name": "Amit",
        "age": 15,
        "subjects": {"Python", "Maths", "English"},
        "marks": (88, 76, 92)
    },
    {
        "name": "Riya",
        "age": 14,
        "subjects": {"Python", "Science", "English"},
        "marks": (91, 85, 89)
    }
]

for student in students:
    print("Name:", student["name"])
    print("Age:", student["age"])
    print("Subjects:", student["subjects"])
    print("Marks:", student["marks"])
    print("Total marks:", sum(student["marks"]))
    print()

Output

Name: Amit
Age: 15
Subjects: {'Python', 'Maths', 'English'}
Marks: (88, 76, 92)
Total marks: 256

Name: Riya
Age: 14
Subjects: {'Python', 'Science', 'English'}
Marks: (91, 85, 89)
Total marks: 265

Final Memory Trick

Collection	Memory Trick
List	Changeable line of items
Tuple	Fixed line of items
Set	Unique items
Frozenset	Fixed unique items
Dictionary	Key-value data

Best beginner rule: Use list for simple collections. Use dictionary for meaningful records. Use set when duplicates must disappear. Use tuple or frozenset when data should not change.

Try the Code in Our Python Editor

Use the embedded Python editor below to run and modify the examples.