Python Sets

In Python, Set is an unordered collection of data type that is iterable, mutable and has no duplicate elements.

Set in Python is equivalent to sets in mathematics. The order of elements in a set is undefined though it may consist of various elements. Elements of a set can be added and deleted, elements of the set can be iterated, various standard operations (union, intersection, difference) can be performed on sets. Besides that, the major advantage of using a set, as opposed to a list, is that it has a highly optimized method for checking whether a specific element is contained in the set.

Creating a Set

Sets can be created by using the built-in set() function with an iterable object or a sequence by placing the sequence inside curly braces, separated by ‘comma’. A set contains only unique elements but at the time of set creation, multiple duplicate values can also be passed. Order of elements in a set is undefined and is unchangeable. Type of elements in a set need not be the same, various mixed up data type values can also be passed to the set.

Note – A set cannot have mutable elements like a list, set or dictionary, as its elements.

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# Python program to demonstrate 
# Creation of Set in Python
  
# Creating a Set
set1 = set()
print("Intial blank Set: ")
print(set1)
  
# Creating a Set with 
# the use of a String
set1 = set("GeeksForGeeks")
print("\nSet with the use of String: ")
print(set1)
  
# Creating a Set with
# the use of Constructor
# (Using object to Store String)
String = 'GeeksForGeeks'
set1 = set(String)
print("\nSet with the use of an Object: " )
print(set1)
  
# Creating a Set with
# the use of a List
set1 = set(["Geeks", "For", "Geeks"])
print("\nSet with the use of List: ")
print(set1)
  
# Creating a Set with 
# a List of Numbers
# (Having duplicate values)
set1 = set([1, 2, 4, 4, 3, 3, 3, 6, 5])
print("\nSet with the use of Numbers: ")
print(set1)
  
# Creating a Set with 
# a mixed type of values
# (Having numbers and strings)
set1 = set([1, 2, 'Geeks', 4, 'For', 6, 'Geeks'])
print("\nSet with the use of Mixed Values")
print(set1)

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Output:

Intial blank Set: 
set()

Set with the use of String: 
{'e', 'r', 'k', 'o', 'G', 's', 'F'}

Set with the use of an Object: 
{'r', 'o', 'e', 'F', 's', 'k', 'G'}

Set with the use of List: 
{'Geeks', 'For'}

Set with the use of Numbers: 
{1, 2, 3, 4, 5, 6}

Set with the use of Mixed Values
{1, 2, 4, 'Geeks', 6, 'For'}

Adding Elements to a Set

Elements can be added to the Set by using built-in add() function. Only one element at a time can be added to the set by using add() method, loops are used to add multiple elements at a time with the use of add() method whereas for addition of two or more elements Update() method is used. The update() method accepts lists, strings, tuples as well as other sets as its arguments. In all of these cases, duplicate elements are avoided.

Note – Lists cannot be added to a set as elements because Lists are not hashable whereas Tuples can be added because tuples are immutable and hence Hashable.

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# Python program to demonstrate 
# Addition of elements in a Set
  
# Creating a Set
set1 = set()
print("Intial blank Set: ")
print(set1)
  
# Adding element to the Set
set1.add(8)
set1.add(9)
set1.add(12)
print("\nSet after Addition of Three elements: ")
print(set1)
  
# Adding elements to the Set
# using Iterator
for i in range(1, 6):
    set1.add(i)
print("\nSet after Addition of elements from 1-5: ")
print(set1)
  
# Adding Tuples to the Set
set1.add((6,7))
print("\nSet after Addition of a Tuple: ")
print(set1)
  
# Addition of elements to the Set
# using Update function
set1.update([10, 11])
print("\nSet after Addition of elements using Update: ")
print(set1)

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Output:

Intial blank Set: 
set()

Set after Addition of Three elements: 
{8, 9, 12}

Set after Addition of elements from 1-5: 
{1, 2, 3, 4, 5, 8, 9, 12}

Set after Addition of a Tuple: 
{1, 2, 3, 4, 5, (6, 7), 8, 9, 12}

Set after Addition of elements using Update: 
{1, 2, 3, 4, 5, (6, 7), 8, 9, 10, 11, 12}

Removing elements from the Set

Elements can be removed from the Set by using built-in remove() function but a KeyError arises if element doesn’t exist in the set. To remove elements from a set without KeyError, use discard(), if the element doesn’t exist in the set, it remains unchanged. Pop() function can also be used to remove and return an element from the set, but it removes only the last element of the set. To remove all the elements from the set, clear() function is used.
Note – If the set is unordered then there’s no such way to determine which element is popped by using the pop() function.

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# Python program to demonstrate 
# Addition of elements in a Set
  
# Creating a Set
set1 = set([1, 2, 3, 4, 5, 6
            7, 8, 9, 10, 11, 12])
print("Intial Set: ")
print(set1)
  
# Removing elements from Set
# using Remove() method
set1.remove(5)
set1.remove(6)
print("\nSet after Removal of two elements: ")
print(set1)
  
# Removing elements from Set
# using Discard() method
set1.discard(8)
set1.discard(9)
print("\nSet after Discarding two elements: ")
print(set1)
  
# Removing elements from Set
# using iterator method
for i in range(1, 5):
    set1.remove(i)
print("\nSet after Removing a range of elements: ")
print(set1)
  
# Removing element from the 
# Set using the pop() method
set1.pop()
print("\nSet after popping an element: ")
print(set1)
  
# Removing all the elements from 
# Set using clear() method
set1.clear()
print("\nSet after clearing all the elements: ")
print(set1)

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Output:

Intial Set: 
{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12}

Set after Removal of two elements: 
{1, 2, 3, 4, 7, 8, 9, 10, 11, 12}

Set after Discarding two elements: 
{1, 2, 3, 4, 7, 10, 11, 12}

Set after Removing a range of elements: 
{7, 10, 11, 12}

Set after popping an element: 
{10, 11, 12}

Set after clearing all the elements: 
set()

Frozen sets in Python are immutable objects that only support methods and operators that produce a result without affecting the frozen set or sets to which they are applied. While elements of a set can be modified at any time, elements of the frozen set remain the same after creation.
If no parameters are passed, it returns an empty frozenset.

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# Python program to demonstrate 
# working of a FrozenSet 
  
# Creating a Set
String = ('G', 'e', 'e', 'k', 's', 'F', 'o', 'r')
  
Fset1 = frozenset(String)
print("The FrozenSet is: ")
print(Fset1)
  
# To print Empty Frozen Set
# No parameter is passed
print("\nEmpty FrozenSet: ")
print(frozenset())

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Set Methods

Function Description
add() Adds an element to a set
remove() Removes an element from a set. If the element is not present in the set, raise a KeyError
clear() Removes all elements form a set
copy() Returns a shallow copy of a set
pop() Removes and returns an arbitary set element. Raise KeyError if the set is empty
update() Updates a set with the union of itself and others
union() Returns the union of sets in a new set
difference() Returns the difference of two or more sets as a new set
difference_update() Removes all elements of another set from this set
discard() Removes an element from set if it is a member. (Do nothing if the element is not in set)
intersection() Returns the intersection of two sets as a new set
intersection_update() Updates the set with the intersection of itself and another
isdisjoint() Returns True if two sets have a null intersection
issubset() Returns True if another set contains this set
issuperset() Returns True if this set contains another set
symmetric_difference() Returns the symmetric difference of two sets as a new set
symmetric_difference_update() Updates a set with the symmetric difference of itself and another

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