What is the difference between a set and a dictionary in Python?

Question

Jayant Kumar · Accepted Answer

Table of Contents
Introduction
In Python, sets and dictionaries are both versatile data structures used to store collections of data. While they share some similarities, they serve different purposes and have distinct characteristics.
What is a Set in Python?
A set is an unordered collection of unique elements. Sets are mutable, meaning you can add or remove items after creation. They do not store duplicate values and do not maintain any specific order.
Example:
# Creating a set
fruits = {'apple', 'banana', 'cherry'}

# Adding an item to the set
fruits.add('orange')

# Removing an item from the set
fruits.remove('banana')

# Checking for membership
print('apple' in fruits)  # Output: True

print(fruits)  # Output: {'apple', 'cherry', 'orange'}

What is a Dictionary in Python?
A dictionary is an unordered collection of key-value pairs. Each key in a dictionary is unique and maps to a specific value. Dictionaries are mutable, allowing you to change, add, or remove key-value pairs.
Example:
# Creating a dictionary
person = {'name': 'Alice', 'age': 25, 'city': 'New York'}

# Accessing a value by key
print(person['name'])  # Output: Alice

# Modifying a value
person['age'] = 26

# Adding a new key-value pair
person['profession'] = 'Engineer'

# Removing a key-value pair
del person['city']

print(person)  # Output: {'name': 'Alice', 'age': 26, 'profession': 'Engineer'}

Key Differences Between Sets and Dictionaries
1. Structure:

Set: Contains only unique elements. It does not store any additional data or mappings.
Dictionary: Contains unique keys each associated with a value. It stores key-value pairs.

2. Accessing Data:

Set: You can only access elements, not through indices or keys, as it does not have an associated value. Membership is checked directly.
Dictionary: You access values through keys. Each key maps to a specific value, which can be retrieved, modified, or deleted.

3. Use Cases:

Set: Ideal for operations involving unique items, such as removing duplicates from a list or performing mathematical set operations like union, intersection, and difference.
Dictionary: Ideal for scenarios where you need to associate keys with values, such as storing user profiles, settings, or mappings between unique identifiers and their associated data.

4. Order:

Set: Unordered collection; the order of elements is not guaranteed.
Dictionary: Maintains insertion order starting from Python 3.7. Prior to Python 3.7, dictionaries were unordered.

5. Performance:

Set: Typically provides fast membership testing and set operations.
Dictionary: Provides fast key-value pair lookups, additions, and deletions.

Practical Examples
Example of Using a Set:
# Set of unique numbers
numbers = {1, 2, 3, 4, 5}

# Adding and removing elements
numbers.add(6)
numbers.discard(2)

# Performing set operations
other_numbers = {4, 5, 6, 7}
print(numbers.union(other_numbers))  # Output: {1, 3, 4, 5, 6, 7}

Example of Using a Dictionary:
# Dictionary of student grades
grades = {'Alice': 'A', 'Bob': 'B', 'Charlie': 'C'}

# Accessing and modifying grades
print(grades['Alice'])  # Output: A
grades['Bob'] = 'A'

# Adding and removing entries
grades['David'] = 'B'
del grades['Charlie']

print(grades)  # Output: {'Alice': 'A', 'Bob': 'A', 'David': 'B'}

Conclusion
Sets and dictionaries are both powerful data structures in Python with distinct uses. Sets are suited for storing unique items and performing set operations, while dictionaries are ideal for associating unique keys with values. Understanding their differences will help you choose the right data structure for your specific needs.

What is the difference between a set and a dictionary in Python?

Table of Contents

Introduction

What is a Set in Python?

What is a Dictionary in Python?

Key Differences Between Sets and Dictionaries

Practical Examples

Conclusion

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