Python Sets

Welcome to The Coding College, your go-to resource for mastering programming concepts! In this guide, we’ll explore Python sets, a unique data structure designed for storing unordered and unindexed collections of items.

By the end of this tutorial, you’ll understand how sets work, their advantages, and how to use them effectively in Python.

What Are Sets in Python?

A set is a collection type in Python that:

  • Is unordered: The items have no defined order.
  • Is unindexed: Items cannot be accessed by position.
  • Contains unique elements: Duplicates are automatically removed.

Sets are useful for tasks like removing duplicates, performing mathematical operations (union, intersection), and efficient membership testing.

How to Create a Set

Sets are defined using curly braces {} or the set() constructor.

Example 1: Creating a Set

# Using curly braces  
my_set = {1, 2, 3, 4}  
print(my_set)  # Output: {1, 2, 3, 4}  

# Using the set() constructor  
another_set = set([1, 2, 2, 3])  
print(another_set)  # Output: {1, 2, 3}

Key Features of Sets

  1. Unordered:
    The order of elements in a set may vary, and it cannot be relied upon.
example_set = {3, 1, 4, 2}  
print(example_set)  # Output: {1, 2, 3, 4} (order may vary)
  1. Unique Elements:
    Duplicate elements are automatically removed.
duplicates = {1, 1, 2, 3, 3}  
print(duplicates)  # Output: {1, 2, 3}
  1. Immutable Elements:
    Sets can only contain immutable (unchangeable) items like numbers, strings, or tuples.
valid_set = {1, "hello", (2, 3)}  
# invalid_set = {1, [2, 3]}  # Raises a TypeError

Accessing Set Items

Since sets are unordered and unindexed, you cannot access elements using an index. However, you can:

1. Iterate Through a Set

Use a for loop to access each item.

my_set = {10, 20, 30}  
for item in my_set:  
    print(item)

2. Check Membership

Use the in keyword to check if an item exists in the set.

my_set = {"apple", "banana", "cherry"}  
print("apple" in my_set)  # Output: True

Set Methods and Operations

Adding and Removing Items

  • add(): Add a single item to the set.
  • update(): Add multiple items (from another set, list, etc.).
  • remove(): Remove an item; raises an error if it doesn’t exist.
  • discard(): Remove an item; doesn’t raise an error if it doesn’t exist.
  • pop(): Remove a random item.

Example:

fruits = {"apple", "banana"}  

# Add items  
fruits.add("cherry")  
print(fruits)  # Output: {'apple', 'banana', 'cherry'}  

# Update items  
fruits.update(["mango", "orange"])  
print(fruits)  # Output: {'apple', 'banana', 'cherry', 'mango', 'orange'}  

# Remove items  
fruits.remove("banana")  
print(fruits)  # Output: {'apple', 'cherry', 'mango', 'orange'}  

# Discard items (safe removal)  
fruits.discard("grape")  # No error raised

Mathematical Set Operations

Python sets support mathematical operations like union, intersection, difference, and symmetric difference.

OperationMethodDescriptionExample
Unionunion()Combines all unique elements from both sets.`{1, 2}
Intersectionintersection()Retains only elements common to both sets.{1, 2} & {2, 3} => {2}
Differencedifference()Returns elements unique to the first set.{1, 2} - {2, 3} => {1}
Symmetric Differencesymmetric_difference()Elements unique to either set, not both.{1, 2} ^ {2, 3} => {1, 3}

Example:

A = {1, 2, 3}  
B = {3, 4, 5}  

# Union  
print(A | B)  # Output: {1, 2, 3, 4, 5}  

# Intersection  
print(A & B)  # Output: {3}  

# Difference  
print(A - B)  # Output: {1, 2}  

# Symmetric Difference  
print(A ^ B)  # Output: {1, 2, 4, 5}

Built-In Functions for Sets

Python provides several built-in functions to work with sets.

FunctionDescriptionExample
len()Returns the number of elements in the set.len({1, 2, 3}) => 3
min()Returns the smallest element.min({10, 20, 30}) => 10
max()Returns the largest element.max({10, 20, 30}) => 30
sum()Returns the sum of all elements.sum({1, 2, 3}) => 6
sorted()Returns a sorted list from the set.sorted({3, 1, 2}) => [1, 2, 3]

Use Cases of Sets

  • Removing Duplicates
    Convert a list with duplicates into a set to keep only unique elements. 
my_list = [1, 2, 2, 3, 4, 4]  
unique = set(my_list)  
print(unique)  # Output: {1, 2, 3, 4}
  • Efficient Membership Testing
    Sets provide faster membership checks compared to lists. 
my_set = {1, 2, 3}  
print(2 in my_set)  # Output: True
  • Mathematical Operations
    Solve problems like finding common or unique items between groups.

Practice Exercises

  1. Create a set from the list [10, 20, 30, 40, 10, 20] and print it.
  2. Add the element "orange" to the set {"apple", "banana"}.
  3. Find the intersection of {1, 2, 3} and {2, 3, 4}.
  4. Use the discard() method to safely remove "blue" from {"red", "blue", "green"}.
  5. Convert the set {3, 1, 4, 2} into a sorted list.

Why Learn Sets with The Coding College?

At The Coding College, we simplify programming concepts and provide hands-on examples to enhance your skills. Python sets are a powerful tool for data analysis and problem-solving. Whether you’re a beginner or an experienced coder, mastering sets will elevate your programming game.

Conclusion

Python sets are versatile and efficient, making them a valuable tool for developers. By practicing the examples and exercises in this guide, you’ll gain a solid understanding of sets and their practical applications.

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