Mastering Python Sets | KSR Datavizon Blog

Learn everything about Python sets in this beginner-to-advanced tutorial. Explore unique elements, set operations, and frozen sets with examples!

What is Python Set?

A group of data is enclosed in a curly =brace {} and each value is separated by a comma.

Key Characteristics of Python Sets

Unique Elements: Sets store unique values, meaning duplicates are not allowed.
Unordered: Sets do not preserve insertion order, but you can sort the elements.
No Indexing or Slicing: You cannot access elements by index or slice in a set.
Heterogeneous Elements: Sets can store elements of different data types.
Mutable: Set objects can be modified after creation (elements can be added or removed).
Mathematical Operations: Sets support operations like union, intersection, and difference.

Python Sets Creation

1. Empty Set:

An empty set can only be created by using the set() function, as {} creates an empty dictionary.

empty_set = set()
print(empty_set)

Output:

set()

2. Using Curly Braces:

my_set = {1, 2, 3, 4}
print(my_set)

Output:

{1, 2, 3, 4}

3. Using the set() function:

# From a list
my_set = set([10, 20, 30])
print(my_set)

# From a range
my_set = set(range(5))
print(my_set)

Output:

{10, 20, 30}
{0, 1, 2, 3, 4}

Note: s={} ==>It is treated as a dictionary but not the empty set.

Common Set Functions

Function	Description	Example	Output
len(set)	Returns the number of elements in a set.	len({1, 2, 3})	3
min(set)	Returns the smallest element in the set.	min({5, 2, 9, 1})	1
max(set)	Returns the largest element in the set.	max({5, 2, 9, 1})	9
sorted(set)	Returns a sorted list from the elements of the set.	sorted({3, 1, 2})	[1, 2, 3]
reversed(set)	Not applicable for sets (as sets are unordered).	N/A	N/A

Note: reversed() does not work with sets because sets are unordered collections, so there is no defined sequence to reverse.

Examples Using All Functions Together:

my_set = {10, 3, 6, 8}

# len() - Get the number of elements in the set
print(f"Length of the set: {len(my_set)}")

# min() - Get the smallest element in the set
print(f"Smallest element: {min(my_set)}")

# max() - Get the largest element in the set
print(f"Largest element: {max(my_set)}")

# sorted() - Sort the set and return a list
print(f"Sorted set: {sorted(my_set)}")

# reversed() - Not applicable, would raise an error if tried.

Output:

Length of the set: 4
Smallest element: 3
Largest element: 10
Sorted set: [3, 6, 8, 10]

Set Methods

Method	Description	Example Code
add(item)	Adds a single element to the set.	s.add(10)
update(iterable)	Adds multiple elements from an iterable.	s.update([20, 30])
remove(item)	Removes the specified element. returns error if not found.	s.remove(10)
discard(item)	Removes the element if present; no error if not found.	s.discard(15)
pop()	Removes and returns an arbitrary element.	s.pop()
clear()	Removes all elements from the set.	s.clear()
union(set2)	Returns the union of two sets.	s.union(s2)
intersection(set2)	Returns the intersection of two sets.	s.intersection(s2)
difference(set2)	Returns the difference between two sets.	s.difference(s2)
symmetric_difference(set2)	Returns elements in either set but not both.	s.symmetric_difference(s2)
issubset(set2)	Checks if one set is a subset of another.	s.issubset(s2)
issuperset(set2)	Checks if one set is a superset of another.	s.issuperset(s2)
isdisjoint(set2)	Checks if two sets have no elements in common.	s.isdisjoint(s2)

** We can see all methods in list by using dir(list) predefined function.

Examples of all methods

1. Adding Elements to a Set

add(item): Adds a single element to the set.
update(iterable): Adds multiple elements from an iterable (e.g., list, set).

s = {1, 2, 3}
s.add(4)  # Adding a single element
print(s)

s.update([5, 6, 7])  # Adding multiple elements from a list
print(s)

Output:

{1, 2, 3, 4}
{1, 2, 3, 4, 5, 6, 7}

2. Removing Elements from a Set

remove(item): Removes the specified element. Returns error if it is not found.
discard(item): Removes the element if present. No error if the element is not found.
pop(): Removes and returns an arbitrary or random element from the set.
clear(): Removes all elements from the set.

s = {1, 2, 3, 4}
s.remove(2)  # Removes 2
print(s)

s.discard(10)  # No error even though 10 is not in the set
print(s) 

print(s.pop())  # Removes and prints an arbitrary element
print(s)

s.clear()  # Clears the set
print(s)

Output:

{1, 3, 4}
{1, 3, 4}
1
{3, 4}
set()

3. Mathematical Set Operations

union(set2): Returns a set containing all elements from both sets.
intersection(set2): Returns a set containing only elements common to both sets.
difference(set2): Returns elements in the first set but not in the second.
symmetric_difference(set2): Returns elements in either set but not in both.

s1 = {1, 2, 3}
s2 = {3, 4, 5}

print(s1.union(s2))
print(s1.intersection(s2))
print(s1.difference(s2))
print(s1.symmetric_difference(s2))

Output:

{1, 2, 3, 4, 5}
{3}
{1, 2}
{1, 2, 4, 5}

s1 = {1, 2, 3}
s2 = {3, 4, 5}

print(s1 | s2)
print(s1 & s2)
print(s1 - s2)
print(s1 ^ s2)

Output:

{1, 2, 3, 4, 5} # Union
{3}             # Intersection
{1, 2}          # Difference
{1, 2, 4, 5}    # Symmetric difference

4. Set Relations and Comparisons

issubset(set2): Checks if one set is a subset of another.
issuperset(set2): Checks if one set is a superset of another.
isdisjoint(set2): Checks if two sets have no common elements.

s1 = {1, 2}
s2 = {1, 2, 3}

print(s1.issubset(s2))
print(s2.issuperset(s1))

s3 = {4, 5}
print(s1.isdisjoint(s3))

Output:

True
True
True

5. Copying Sets

copy(): it creates and returns a shallow copy of a set.

s1 = {1, 2, 3}
s_copy = s1.copy()
print(s_copy)

Output:

{1,2,3}

Membership Operators: (in, not in)

We can check whether a given element exists in a set or not using these operators

in: Checks if an element is present in the set.
not in: Checks if an element is absent from the set.

s = set("apple")
print(s)
print('a' in s)
print('z' in s)

Output:

{'p', 'a', 'e', 'l'}
True
False

Set Comprehension

We can generate sets using set comprehension just like list comprehension but with curly braces {}.

# Set of squares
st1 = {x*x for x in range(5)}
print(st1)

# Set of powers of 2
st2 = {2**x for x in range(2, 10, 2)}
print(st2)

Output:

{0, 1, 4, 9, 16}
{16, 256, 64, 4}

Frozen Set

A frozen set is a data type that represents an immutable version of a set. It is similar to a regular set, but unlike sets, frozen sets cannot be modified after creation, making them hashable and usable as dictionary keys or set elements.

Immutable: Once created, you cannot add or remove elements from a frozen set.
Hashable: Frozen sets can’t be changed, so you can safely use them as keys in dictionaries or as items inside other sets.
Unordered: Like regular sets, frozen sets do not maintain the order of elements.
No Duplicates: They cannot contain duplicate elements.

Creating a Frozen Set:

We can create a frozen set using the frozenset() pre-defined function:

# Creating a frozen set from a list
frozen_set = frozenset([1, 2, 3, 4])
print(frozen_set)

# Creating a frozen set from a string
frozen_set_from_str = frozenset("hello")
print(frozen_set_from_str)

Output:

frozenset({1, 2, 3, 4})
frozenset({'o', 'l', 'e', 'h'})

Conclusion

Sets are powerful tools in Python for handling collections of unique elements. Their built-in operations make them efficient for tasks involving membership tests, unions, intersections, and more.