SETS

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Python - Sets

A set is a collection which is unordered and unindexed. In Python sets are written with curly brackets.

create a set :

set={"apple","banana","cherry"}
print(set)
====O/P====
{'apple', 'banana', 'cherry'}

Note: Sets are unordered, so you cannot be sure in which order the items will appear.

Access Items :

You cannot access items in a set by referring to an index, since sets are unordered the items has no index.

But you can loop through the set items using a for loop, or ask if a specified value is present in a set, by using the in keyword.

set={"apple","banana","cherry"}
for i in set:
    print(set)
====O/P====
{'apple', 'banana', 'cherry'}
{'apple', 'banana', 'cherry'}
{'apple', 'banana', 'cherry'}

Check if "banana" is present in the set :

set={"apple","banana","cherry"}
print("banana" in set)

====O/P====
True

Change Items :

Once a set is created, you cannot change its items, but you can add new items.

Add Items :

To add one item to a set use the add() method.

To add more than one item to a set use the update() method.

Using add() :

set={"apple","banana","cherry"}
set.add("orange")
print(set) 

====O/P====
{'banana', 'orange', 'cherry', 'apple'}

Using update( ) :

set={"apple","banana","cherry"}
set.update(["orange","papaya","strawberry"])
print(set)

====O/P====

{'strawberry', 'cherry', 'orange', 'papaya', 'banana', 'apple'}
    

Get the Length of a Set :

To determine how many items a set has, use the len( ) method.

set={"a","e","i","o","u"}
print(len(set))

====O/P====
5

Remove Item :

To remove an item in a set, use the remove( ), or the discard( ) method.

set={"a","e","i","o","u"}
set.remove("a")
print(set)

====O/P====
{'e', 'o', 'i', 'u'}

Note: If the item to remove does not exist, remove() will raise an error.

Remove using discard( ) :

set={"a","e","i","o","u"}
set.discard("u")
print(set)

====o/p====
{'e', 'o', 'a', 'i'}

Note: If the item to remove does not exist, discard( ) will NOT raise an error.

We can also use the pop( ), method to remove an item,actually this method will remove the last item.But sets being unordered, we will not know what item gets removed.

The return value of the pop( ) method is the removed item.

set={"a","e","i","o","u"}
x=set.pop()
print(x)#removed item
print(set)# set after removal

====O/P====
o
{'u', 'i', 'a', 'e'}

Note: Sets are unordered, so when using the pop( ) method, you will not know which item that gets removed.

The clear( ) method empties the set.

set={"a","e","i","o","u"}
set.clear()
print(set)

====O/P====
set( )

The del keyword will delete the set completely.

set={"a","e","i","o","u"}
del set
print(set)

====o/p====
#it raises an error because set gets deleted
or we will get output as <class 'set'>

Join Two Sets :

There are several ways to join two or more sets in Python.

we can use the union() method that returns a new set containing all items from both sets, or the update() method that inserts all the items from one set into another:

set1={"a","e","i","o","u"}
set2={1,2,3,4,5}
set3=set1.union(set2)
print(set3)

===o/p===
{1, 2, 3, 4, 'o', 5, 'i', 'u', 'e', 'a'}

set1={"a","e","i","o","u"}
set2={1,2,3,4,5}
set1.update(set2)
print(set1)

====o/p====
{1, 2, 'e', 3, 4, 5, 'a', 'i', 'o', 'u'}

Note: Both union() and update() will exclude any duplicate items.

The set() Constructor :

It is also possible to use the set() constructor to make a set.

set=(("a","e","i","o","u")) #note the double brackets
print(set)

===o/p===
('a', 'e', 'i', 'o', 'u')

Set Methods :

Method	Description
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