Tutorial
Home

Python Set

Python Set Tutorial

Welcome to this comprehensive tutorial on Python sets, brought to you by codeswithpankaj.com. In this tutorial, we will explore various aspects of sets in Python, covering their syntax, usage, and practical examples. By the end of this tutorial, you will have a thorough understanding of how to use sets effectively in your Python programs.

Table of Contents

  1. Introduction to Sets

  2. Creating Sets

  3. Accessing Set Elements

  4. Modifying Sets

    • Adding Elements

    • Removing Elements

  5. Set Operations

    • Union

    • Intersection

    • Difference

    • Symmetric Difference

  6. Set Methods

    • add()

    • update()

    • remove()

    • discard()

    • pop()

    • clear()

    • copy()

    • union()

    • intersection()

    • difference()

    • symmetric_difference()

    • issubset()

    • issuperset()

    • isdisjoint()

  7. Frozen Sets

  8. Practical Examples

  9. Common Pitfalls and Best Practices

1. Introduction to Sets

Sets are an unordered collection of unique items. They are used to store multiple items in a single variable, and they automatically remove duplicates. Sets are mutable, which means you can add or remove items from them.

Why Sets are Important

Sets are useful for membership testing, removing duplicates from a sequence, and performing mathematical operations like union, intersection, difference, and symmetric difference.

2. Creating Sets

A set is created by placing all the items (elements) inside curly braces {}, separated by commas, or by using the set() function.

Syntax

set_name = {item1, item2, item3, ...}

Examples

# Creating a set of integers
numbers = {1, 2, 3, 4, 5}

# Creating a set of programming languages
languages = {"Python", "Java", "C++"}

# Creating a mixed set
mixed_set = {1, "Python", 3.5, True}

# Creating a set using the set() function
set_from_list = set([1, 2, 3, 4, 5])

3. Accessing Set Elements

Sets do not support indexing, slicing, or other sequence-like behavior. You cannot access elements in a set by index, but you can loop through the set items using a for loop.

Example

# Accessing elements using a for loop
for language in languages:
    print(language)

4. Modifying Sets

You can modify sets by adding or removing elements.

Adding Elements

add()

The add() method adds a single element to the set.

# Adding elements using add()
languages.add("JavaScript")
print(languages)  # Output: {'Python', 'Java', 'C++', 'JavaScript'}

update()

The update() method adds multiple elements to the set. You can pass a list, tuple, or another set.

# Adding elements using update()
languages.update(["Ruby", "Go"])
print(languages)  # Output: {'Python', 'Java', 'C++', 'JavaScript', 'Ruby', 'Go'}

Removing Elements

remove()

The remove() method removes the specified element from the set. If the element is not found, it raises a KeyError.

# Removing elements using remove()
languages.remove("Java")
print(languages)  # Output: {'Python', 'C++', 'JavaScript', 'Ruby', 'Go'}

discard()

The discard() method removes the specified element from the set. If the element is not found, it does not raise an error.

# Removing elements using discard()
languages.discard("C++")
print(languages)  # Output: {'Python', 'JavaScript', 'Ruby', 'Go'}

pop()

The pop() method removes and returns a random element from the set. Sets are unordered, so you do not know which item gets removed.

# Removing elements using pop()
random_language = languages.pop()
print(random_language)  # Output: a random language
print(languages)  # Output: set with one less element

clear()

The clear() method removes all elements from the set.

# Clearing the set
languages.clear()
print(languages)  # Output: set()

5. Set Operations

Union

The union of two sets is a set containing all unique elements from both sets. You can use the | operator or the union() method.

# Union of sets
set1 = {1, 2, 3}
set2 = {3, 4, 5}
union_set = set1 | set2
print(union_set)  # Output: {1, 2, 3, 4, 5}

Intersection

The intersection of two sets is a set containing only the elements that are common to both sets. You can use the & operator or the intersection() method.

# Intersection of sets
intersection_set = set1 & set2
print(intersection_set)  # Output: {3}

Difference

The difference of two sets is a set containing the elements of the first set that are not in the second set. You can use the - operator or the difference() method.

# Difference of sets
difference_set = set1 - set2
print(difference_set)  # Output: {1, 2}

Symmetric Difference

The symmetric difference of two sets is a set containing the elements that are in either of the sets, but not in both. You can use the ^ operator or the symmetric_difference() method.

# Symmetric difference of sets
symmetric_difference_set = set1 ^ set2
print(symmetric_difference_set)  # Output: {1, 2, 4, 5}

6. Set Methods

add()

Adds an element to the set.

languages.add("JavaScript")
print(languages)  # Output: {'Python', 'Java', 'JavaScript'}

update()

Adds multiple elements to the set.

languages.update(["Ruby", "Go"])
print(languages)  # Output: {'Python', 'Java', 'JavaScript', 'Ruby', 'Go'}

remove()

Removes the specified element from the set. Raises a KeyError if the element is not found.

languages.remove("Java")
print(languages)  # Output: {'Python', 'JavaScript', 'Ruby', 'Go'}

discard()

Removes the specified element from the set. Does not raise an error if the element is not found.

languages.discard("Ruby")
print(languages)  # Output: {'Python', 'JavaScript', 'Go'}

pop()

Removes and returns a random element from the set.

random_language = languages.pop()
print(random_language)  # Output: a random language
print(languages)  # Output: set with one less element

clear()

Removes all elements from the set.

languages.clear()
print(languages)  # Output: set()

copy()

Returns a shallow copy of the set.

languages_copy = languages.copy()
print(languages_copy)  # Output: set()

union()

Returns a set containing all unique elements from both sets.

set1 = {1, 2, 3}
set2 = {3, 4, 5}
union_set = set1.union(set2)
print(union_set)  # Output: {1, 2, 3, 4, 5}

intersection()

Returns a set containing only the elements that are common to both sets.

intersection_set = set1.intersection(set2)
print(intersection_set)  # Output: {3}

difference()

Returns a set containing the elements of the first set that are not in the second set.

difference_set = set1.difference(set2)
print(difference_set)  # Output: {1, 2}

symmetric_difference()

Returns a set containing the elements that are in either of the sets, but not in both.

symmetric_difference_set = set1.symmetric_difference(set2)
print(symmetric_difference_set)  # Output: {1, 2, 4, 5}

issubset()

Returns True if the set is a subset of another set.

set3 = {1, 2}
print(set3.issubset(set1))  # Output: True

issuperset()

Returns True if the set is a superset of another set.

print(set1.issuperset(set3))  # Output: True

isdisjoint()

Returns True if the sets have no elements in common.

set4 = {6, 7}
print(set1.isdisjoint(set4))  # Output: True

7. Frozen Sets

Frozen sets are immutable sets. They are created using the frozenset() function. Once created, elements cannot be added or removed.

Creating a Frozen Set

# Creating a frozen set
frozen_set = frozenset([1,

 2, 3, 4, 5])
print(frozen_set)  # Output: frozenset({1, 2, 3, 4, 5})

Using Frozen Sets

Frozen sets support the same methods as regular sets, except for methods that modify the set (like add(), remove(), etc.).

# Checking membership in a frozen set
print(3 in frozen_set)  # Output: True

# Union of frozen sets
another_frozen_set = frozenset([4, 5, 6, 7])
union_frozen_set = frozen_set.union(another_frozen_set)
print(union_frozen_set)  # Output: frozenset({1, 2, 3, 4, 5, 6, 7})

8. Practical Examples

Example 1: Removing Duplicates from a List

You can use a set to remove duplicates from a list.

# Removing duplicates using a set
numbers = [1, 2, 2, 3, 4, 4, 5]
unique_numbers = list(set(numbers))
print(unique_numbers)  # Output: [1, 2, 3, 4, 5]

Example 2: Set Operations on Lists

Perform set operations like union, intersection, and difference on lists.

# Union of lists
list1 = [1, 2, 3]
list2 = [3, 4, 5]
union_list = list(set(list1) | set(list2))
print(union_list)  # Output: [1, 2, 3, 4, 5]

# Intersection of lists
intersection_list = list(set(list1) & set(list2))
print(intersection_list)  # Output: [3]

# Difference of lists
difference_list = list(set(list1) - set(list2))
print(difference_list)  # Output: [1, 2]

Example 3: Finding Common Elements

Find common elements between two lists.

# Finding common elements
list1 = ["Python", "Java", "C++"]
list2 = ["Java", "C++", "JavaScript"]
common_elements = list(set(list1) & set(list2))
print(common_elements)  # Output: ['Java', 'C++']

9. Common Pitfalls and Best Practices

Pitfalls

  1. Unordered Nature: Sets are unordered, so the elements do not have a fixed order.

  2. Mutability: While sets are mutable, frozen sets are not. Choose the appropriate type based on your needs.

  3. Unique Elements: Sets automatically remove duplicates, which might not be desired in some cases.

Best Practices

  1. Use Sets for Membership Testing: Sets are optimized for membership testing, so use them when you need to check for the presence of an element.

  2. Use Descriptive Names: Use meaningful names for sets and their elements to improve code readability.

  3. Leverage Set Operations: Use set operations like union, intersection, and difference to simplify your code.

# Using sets effectively
languages = {"Python", "Java", "C++"}
web_languages = {"JavaScript", "HTML", "CSS", "Python"}

# Finding common languages
common_languages = languages.intersection(web_languages)
print(common_languages)  # Output: {'Python'}

This concludes our detailed tutorial on Python sets. We hope you found this tutorial helpful and informative. For more tutorials and resources, visit codeswithpankaj.com. Happy coding!

PreviousPython TupleNextPython String

Last updated