Python Set – Things You MUST Know

Python set is an un-ordered and un-indexed collection of elements.

  • Every element is unique.
  • The set contains elements that are un-ordered.
  • No duplicates are allowed.
  • The set itself is mutable i.e. one can add/remove items(elements) from it.
  • Unlike arrays, wherein the elements are stored in order, the order of elements in a set is not defined.
  • The elements in the set are not stored in their order of appearance in the set.

Creation of Sets in Python

Set can be created by placing all the elements within curly braces {}, separated by a comma. They can also be created by using the built-in function set().

The elements can be of different data types, but a Set doesn’t support mutable elements. Sets are unordered, so one can’t be sure of the order of elements in which they will appear.

Example: Creation of Sets

Days=set(["Mon","Tue","Wed","Thu","Fri","Sat","Sun"])
Fruits = {"apple", "banana", "cherry"}
Name=set('Quit')
print(Name)
print(Fruits)
print(Days)

Output:

{‘u’, ‘Q’, ‘i’, ‘t’}
{‘cherry’, ‘banana’, ‘apple’}
{‘Sun’, ‘Wed’, ‘Mon’, ‘Thu’, ‘Tue’, ‘Sat’, ‘Fri’}

Recommended Readings:

  1. List in Python
  2. Array in Python
  3. Python Tuple

Access elements from the Python Set

Since, sets are un-ordered and un-indexed, one cannot access the elements by referring to its index, unlike arrays.

The elements of the Sets can be accessed by either of the following ways:

  1. Iterate through the loop of the set items using a for loop .
  2. Check whether a specified value is present in a set, by using the in keyword .

Example: Accessing elements from a Set

Fruits = {"apple", "mango", "cherry"}
for a in Fruits:
  print(a)
print("banana" in Fruits)
print("mango" in Fruits)

Output:

mango
cherry
apple
False
True

Add elements to a Python Set

We can add elements to a set by using add() function. In case, we require to add more elements we need to use update() method to do so.

Example: Addition of elements to a Set

Fruits = {"apple", "mango", "cherry"}

Fruits.add("grapes")

print(Fruits)

Fruits.update(["banana", "orange", "strawberry"])

print(Fruits)

Output:

{‘cherry’, ‘apple’, ‘mango’, ‘grapes’}
{‘strawberry’, ‘cherry’, ‘apple’, ‘orange’, ‘banana’, ‘mango’, ‘grapes’}

Removal of elements from a Set

We can delete the items from the Set using either of the following methods:

  1. By using remove() method
  2. By using discard() method
  3. By using clear() method – deletes all the elements from the Set
  4. By using del() method – deletes the entire Set

Example 1: Using remove() method

Fruits = {"apple", "grapes", "cherry"}

Fruits.remove("grapes")

print(Fruits)

Output:

{‘cherry’, ‘apple’}

Example 2: Using discard() method

Fruits = {"apple", "grapes", "cherry"}

Fruits.discard("grapes")

print(Fruits)

Output:

{‘cherry’, ‘apple’}

Example 3: Using clear() method

Fruits = {"apple", "grapes", "cherry"}

Fruits.clear()

print(Fruits)

Output:

set()

Example 4: Using del() method

Fruits = {"apple", "grapes", "cherry"}

del Fruits

print(Fruits)

Output:

 Traceback (most recent call last):
 File "main.py", line 5, in <module>
 print(Fruits) 
NameError: name 'Fruits' is not defined

Methods in Sets

MethodDescription
add()Adds an element to the set
clear()Removes all the elements from the set
copy()Returns a copy of the set
difference()Returns a set containing the difference between two or more sets
difference_update()Removes the items in this set that are also included in another, specified set
discard()Remove the specified item
intersection()Returns a set, that is the intersection of two other sets
intersection_update()Removes the items in this set that are not present in other, specified set(s)
isdisjoint()Returns whether two sets have a intersection or not
issubset()Returns whether another set contains this set or not
issuperset()Returns whether this set contains another set or not
pop()Removes an element from the set
remove()Removes the specified element
symmetric_difference()Returns a set with the symmetric differences of two sets
symmetric_difference_update()inserts the symmetric differences from this set and another
union()Return a set containing the union of sets
update()Update the set with the union of this set and others

Set Operations in Python

Sets are used to carry out mathematical functionality set operations such as union, difference, intersection, and symmetric difference.

Set Union – Inclusion of all elements from both the sets.

Union operation is performed by either of the following methods:

  • By using | operator
  • By using union() method

Example: Union of Sets

X = {1, 2, 3}
Y = {6, 7, 8}

print(X | Y)
print(Y.union(X))

Output:

{1, 2, 3, 6, 7, 8}
{1, 2, 3, 6, 7, 8}

Set Intersection – Inclusion of elements that are common to both the sets.

Intersection operation is performed by either of the following methods:

  • By using & operator
  • By using intersection() method

Example: Intersection of Sets

X = {1, 2, 3}
Y = {3, 2, 8}

print(X & Y)
print(Y.intersection(X))

Output:

{2, 3}
{2, 3}

Set Difference – Inclusion of elements from either of the sets.

(A – B) contains the elements that are only in set A but not in set B.

(B – A) contains the elements that are only in set B but not in set A.

Difference operation is performed by either of the following methods:

  • By using - operator
  • By using difference() method

Example: Difference of Sets

X = {1, 2, 3}
Y = {3, 2, 8}

print(X - Y)

print(Y.difference(X))

Output:

{1}
{8}

Set Symmetric Difference – Inclusion of elements from both the sets except the common elements of the sets

Symmetric Difference operation is performed by either of the following methods:

  • By using ^ operator
  • By using symmetric_difference() method

Example: Symmetric Difference of Sets

X = {1, 2, 3, 9, 0}
Y = {3, 2, 8, 7, 5}

print(X ^ Y)

print(Y.symmetric_difference(X))

Output:

{0, 1, 5, 7, 8, 9}
{0, 1, 5, 7, 8, 9}

References