Sets in Python Programming

Data Structures in Python

What is Sets in Python?

A Set is an unordered collection of unique elements. We cannot add a duplicate element in a set.

A Set can contain elements of different data types. We can only add immutable elements in a set, we cannot update or change an element in a set, but we can add or remove elements from it.

Sets are mutable we can add or remove elements in a set once it is created.

Sets are useful when we are working with set related problems in mathematics like union, intersection, difference or symmetric difference, etc.

set_name = {elements1,element2,...}

a = {5,8,6,2,9}     # A set with five elements in it

Creating an Integer Type Set

A python program to show how to create and display an integer type set in python.

a={15,2,49,51,34}

# printing the elements from an integer type set
for x in a:
    print(x)

2
34
15
49
51

Note: We can see that the elements are not displayed in order as it is store in the set. It proves that sets are unordered, as stated in its definition.

Creating a Floating Point Number Type Set

A python program to show how to create and display a floating point number type set in python.

a={18.23,24.11,564.2369,44.17,98.513}

# printing the elements from a floating point number type set
for x in a:
    print(x)

44.17
18.23
98.513
564.2369
24.11

Creating a Character Type Set

A python program to show how to create and display a character type set in python.

a={'a','e','i','o','u'}

# printing the elements from a character type set
for x in a:
    print(x)

o
a
i
u
e

Creating a String Type Set

A python program to show how to create and display a string type set in python.

a={'apple','ball','cat','dog','eagle'}

# printing the elements from a string type set
for x in a:
    print(x)

apple
eagle
ball
cat
dog

Creating a Set of Different Types of Elements

A python program to show how to create and display a set of different types of elements in python.

a={15,'Henry','2A',56,81,74,70.33,'B'}

# printing the elements from a set having different types of elements
for x in a:
    print(x)

74
70.33
15
81
Henry
2A
56
B

Create Sets from Existing Sequences

A python program to show how to create sets from existing sequences. A sequence can be any kind of sequence including string, tuples and lists.

str='Python'    # A String
name=['Allen','Peter','Henry','Stephen']    # A List
t=(12,89,63)    # A Tuple

S1=set(str)        # Creating a set from a String
S2=set(name)       # Creating a set from another List
S3=set(t)          # Creating a set from a Tuple

print(S1)
print(S2)
print(S3)

{'t', 'n', 'y', 'o', 'h', 'P'}
{'Henry', 'Allen', 'Peter', 'Stephen'}
{89, 12, 63}

Creating an Empty Set

We can also create an empty set that does not contain elements at the time of declaration. See the example given below.

a = set()          # An empty set
print(a)

set()

Use of Membership Operator in Set

Both in and not in operators works on Set just like they work for other sequences such as strings, lists and tuples. The in operator tells if an element is present in the set or not and not in does the opposite. See the example given below.

a={15,2,49,51,86}

print(a)
if (49 in a) == True:
    print('49 is prenest in the set')
else:
    print('49 is not prenest in the set')

if (70 not in a) == True:
    print('70 is not prenest in the set')
else:
    print('70 is prenest in the set')

{2, 15, 49, 51, 86}
49 is prenest in the set
70 is not prenest in the set

Set Methods

Set methods in Python are a collection of useful functions used to perform a specific task on a set. Let's see all the important set methods one by one with examples.

add() Method

The add() method adds an element to an existing set. It does not add the element if the element is already present in the set.

a={11,9,26,34,53}
print('Original Set: ',a)
a.add(88)
print('Set after adding 88: ',a)

Original Set:  {34, 9, 11, 53, 26}
Set after adding 88:  {34, 9, 11, 53, 88, 26}

discard() Method

The discard() method removes an element from an existing set if it is a member element. It does nothing if the element is not a member element.

a={11,9,26,34,53}
print('Original Set: ',a)
a.discard(34)
print('Set after removing 34: ',a)

Original Set:  {34, 9, 11, 53, 26}
Set after removing 34:  {9, 11, 53, 26}

clear() Method

The clear() method removes all the elements from an existing set. After removing all the elements the set becomes an empty set.

a={11,9,26,34,53}
print('Original Set: ',a)
a.clear()
print('Set a after removing all the elements: ',a)

Original Set:  {34, 9, 11, 53, 26}
Set a after removing all the elements:  set()

pop() Method

The pop() method remove and returns an element from an existing set based on random choice. Raises KeyError if the set is empty.

a={11,9,26,34,53}
print('Original Set: ',a)
x=a.pop()
print("Element removed: ",x)
print('Set a after removing the element: ',a)

Original Set:  {34, 9, 11, 53, 26}
Element removed:  34
Set a after removing the element:  {9, 11, 53, 26}

copy() Method

The copy() method returns a shallow copy of an existing set. A shallow copy means an exact copy of a set.

a={11,9,26,34,53}
print('Original Set: ',a)
b=a.copy()
print("Shallow Copy Set: ",b)

Original Set:  {34, 9, 11, 53, 26}
Shallow Copy Set:  {34, 53, 9, 26, 11}

union() Method

The union() method returns the union of sets as a new set. The union of two or more sets is a set that contains all the elements present either in set A or set B.

a={2,1,3,5,4}
b={5,7,6,8,1}
c={94,'Allen',75}
d={'Peter','Allen','Sam','Albert'}

print('Set a: ',a)
print('Set b: ',b)
print('Set c: ',c)
print('Set d: ',d)

e=a.union(b)
print('Set e (Union of Set a and b): ',e)

f=b.union(c,d)
print('Set f (Union of Set b, c and d): ',f)

Set a:  {1, 2, 3, 4, 5}
Set b:  {1, 5, 6, 7, 8}
Set c:  {'Allen', 75, 94}
Set d:  {'Allen', 'Sam', 'Peter', 'Albert'}
Set e (Union of Set a and b):  {1, 2, 3, 4, 5, 6, 7, 8}
Set f (Union of Set b, c and d):  {1, 'Sam', 'Peter', 5, 6, 7, 8, 75, 'Allen', 'Albert', 94}

update() Method

The update() method add elements from other specified sequences like (sets, lists, tuples) which are not present in the set that is to be updated.

a={2,1,3,5,4}
b=[94,'Allen',75,1,4]
c=(56,89,34,75)
print('Set a: ',a)
print('List b: ',b)
print('Tuple c: ',c)

a.update(b,c)
print('Set a after update: ',a)

Set a:  {1, 2, 3, 4, 5}
List b:  [94, 'Allen', 75, 1, 4]
Tuple c:  (56, 89, 34, 75)
Set a after update:  {1, 2, 3, 4, 5, 34, 'Allen', 75, 56, 89, 94}

intersection() Method

The intersection() method returns the intersection of two sets as a new set. The intersection set is a set that contains the common elements present in both sets.

a={2,1,3,5,4}
b={94,'Allen',75,1,4}
print('Set a: ',a)
print('Set b: ',b)

c=a.intersection(b)
print('Set c (intersection set): ',c)

Set a:  {1, 2, 3, 4, 5}
Set b:  {1, 4, 'Allen', 75, 94}
Set c (intersection set):  {1, 4}

intersection_update() Method

The intersection_update() method updates a set with the intersection of itself and another specified sets.

a={2,1,3,5,4}
b={94,'Allen',75,10,17,4}
c={75,4,'Sam',17}
print('Set a: ',a)
print('Set b: ',b)
print('Set c: ',c)

a.intersection_update(b,c)
print('Set a after intersection update from Set a,b,c: ',a)

Set a:  {1, 2, 3, 4, 5}
Set b:  {4, 10, 75, 'Allen', 17, 94}
Set c:  {'Sam', 75, 4, 17}
Set a after intersection update from Set a,b,c:  {4}

Note: Here set a is updated with the value 4 which is the intersection (common) value in all the three sets a,b and c.

difference() Method

The difference() method returns the difference between two or more sets as a new set. The new set contains all elements that are in this set but not the others.

a={2,1,3,5,4}
b={94,'Allen',75,10,17}
c={75,4,'Sam',17}
print('Set a: ',a)
print('Set b: ',b)
print('Set c: ',c)

d=a.difference(b,c)
print('Difference: Elements present in Set a but not in Set b or c: ',d)

Set a:  {1, 2, 3, 4, 5}
Set b:  {10, 75, 17, 94, 'Allen'}
Set c:  {17, 'Sam', 75, 4}
Difference: Elements present in Set a but not in Set b or c:  {1, 2, 3, 5}

difference_update() Method

The difference_update() method remove elements from this set which is also present in other sets.

a={2,1,3,5,4}
b={94,'Allen',75,10,5}
c={75,4,'Sam',5}
print('Set a: ',a)
print('Set b: ',b)
print('Set c: ',c)

a.difference_update(b,c)
print('Set a after difference update from Set b and c: ',a)

Set a:  {1, 2, 3, 4, 5}
Set b:  {5, 'Allen', 10, 75, 94}
Set c:  {75, 4, 5, 'Sam'}
Set a after difference update from Set b and c:  {1, 2, 3}

symmetric_difference() Method

The symmetric_difference() method returns the symmetric difference of two sets as a new set. The method takes only one set as an arguments. The Symmetric Difference of two sets A and B is calculated as (Set A - Set B) union (Set B - Set A). In other words, it returns a new set having all elements that are present either in Set A or Set B but not both.

a={1,2,3,4,5,6,7}
b={1,3,5,6,7,8,9}
print('Set a: ',a)
print('Set b: ',b)

c=a.symmetric_difference(b)
print('Set c after symmetric difference of Set a and b: ',c)

Set a:  {1, 2, 3, 4, 5, 6, 7}
Set b:  {1, 3, 5, 6, 7, 8, 9}
Set c after symmetric difference of Set a and b:  {2, 4, 8, 9}

Here Set a - Set b is {2, 4} and Set b - Set a is {8, 9} and the union of both the output is {2, 4, 8, 9}.

symmetric_difference_update() Method

The symmetric_difference_update() method updates a set with the symmetric difference of itself and another. In other words, it updates Set A with elements that are present either in Set A or Set B but not both.

a={1,2,3,4,5,6,7}
b={1,3,5,6,7,8,9}
print('Set a: ',a)
print('Set b: ',b)

a.symmetric_difference_update(b)
print('Set a after symmetric difference update with Set b: ',a)

Set a:  {1, 2, 3, 4, 5, 6, 7}
Set b:  {1, 3, 5, 6, 7, 8, 9}
Set a after symmetric difference update with Set b:  {2, 4, 8, 9}

isdisjoint() Method

The isdisjoint() method returns True if two sets have a null intersection, which means no common elements exist in the sets.

a={1,2,3,4}
b={5,6,7,8}
c={9,7,38,42}
print('Set a: ',a)
print('Set b: ',b)
print('Set c: ',c)

d=a.isdisjoint(b)
print('Is Set a and b are disjoint ',d)

e=b.isdisjoint(c)
print('Is Set b and c are disjoint ',e)

Set a:  {1, 2, 3, 4}
Set b:  {8, 5, 6, 7}
Set c:  {9, 42, 38, 7}
Is Set a and b are disjoint  True
Is Set b and c are disjoint  False

issuperset() Method

The issuperset() method returns True if all the elements of another set are present in this set. For example, Set A is a superset of another Set B if all the elements of Set B are elements of Set A also.

a={1,2,3,4}
b={5,6,7,8,9,75,42,86,38}
c={9,7,38,42}
print('Set a: ',a)
print('Set b: ',b)
print('Set c: ',c)

d=b.issuperset(a)
print('Is all the elements of Set a are elements of Set b ',d)

e=b.issuperset(c)
print('Is all the elements of Set c are elements of Set b ',e)

Set a:  {1, 2, 3, 4}
Set b:  {5, 6, 7, 8, 9, 42, 75, 38, 86}
Set c:  {9, 42, 38, 7}
Is all the elements of Set a are elements of Set b  False
Is all the elements of Set c are elements of Set b  True

issubset() Method

The issubset() method returns True if all the elements of a particular set are present in another set. For example, Set A is a subset of another Set B if all the elements of Set A are elements of Set B also.

a={1,2,3,4}
b={5,6,7,8,9,75,42,86,38}
c={9,7,38,42}
print('Set a: ',a)
print('Set b: ',b)
print('Set c: ',c)

d=c.issubset(b)
print('Is all the elements of Set c are elements of Set b ',d)

e=a.issubset(b)
print('Is all the elements of Set a are elements of Set b ',e)

Set a:  {1, 2, 3, 4}
Set b:  {5, 6, 7, 8, 9, 42, 75, 38, 86}
Set c:  {9, 42, 38, 7}
Is all the elements of Set c are elements of Set b  True
Is all the elements of Set a are elements of Set b  False

Functions to Process Sets

There are some useful functions available in python that we can apply on a set. The difference between Function and Method is that a Function is called directly with its name but a Method is called on objects only.

Let's see the functions given below with examples.

max() Function

The max() function returns the biggest element in a set.

a={11,91,57,34,26,97,63,18}
print('Set: ',a)
print('Biggest element is :',max(a))

Set:  {97, 34, 11, 18, 57, 26, 91, 63}
Biggest element is : 97

min() Function

The min() function returns the smallest element in a set.

a={11,9,57,34,5,97,63,10}
print('Set: ',a)
print('Smallest element is :',min(a))

Set:  {97, 34, 5, 9, 10, 11, 57, 63}
Smallest element is : 5

len() Function

The len() function returns the total numbers of elements present in a set.

a={11,91,57,34,26,97,63,18}
print('Set: ',a)
print('Total number of elements :',len(a))

Set:  {97, 34, 11, 18, 57, 26, 91, 63}
Total number of elements : 8