Sets

Sets are used to store multiple items in a single variable

Sets are one of 4 built-in data types in Python used to store collections of data

Sets are written with curly brackets { }

A set is an unordered, immutable, unindexed and do not allow duplicate values

myset = {"red", "green", "blue"}
print(myset)  #Output: {'blue', 'green', 'red'}

Do not allow duplicate values

myset = {"red", "green", "blue","red", "green"}  #remove duplicate value
print(myset)  #Output: {"red", "green", "blue"}

Unordered & Unindexed

Unordered means that the items in a set do not have a defined order so it's unindexed which means can't access an item in the set by the index

myset = {"red", "green", "blue"}
print(myset)  #Output: {'blue', 'green', 'red'}

In the above code snippet, the given order is "red", "green" & "blue" but the output order is 'blue', 'green' & 'red' that's why we say the set is unordered

Immutable

Every set element is unique (no duplicates) and must be immutable (cannot be changed).

thisset = {"one", "two", "three"}
thisset[1] = "four"

print(thisset) #Output: TypeError: 'set' object does not support item assignment

However, a set itself is mutable. We can add or remove items from it.

thisset = {"one", "two", "three"}

thisset.add("four")
print(thisset)      #Output: {'four', 'two', 'one', 'three'}

thisset.update({"five", "six"})
print(thisset)      #Output: {'two', 'six', 'five', 'four', 'one', 'three'}

Set Methods

Python has a set of built-in methods that you can use on sets.

NOTE: We are not going to see all the methods as some of them are similar to the list methods.

Venn Diagram

If you have ever seen a Venn diagram in your school.

For Example, two circles are overlapping each other and you may find a union and intersection value between two or three given sets that are similar to these methods.

difference()

returns a set containing the difference between two or more sets

my_set = {1,2,3,4,5,6}
your_set = {4,5,6,7,8,9}

result_set = my_set.difference(your_set)
print(result_set)       #Output: {1, 2, 3}

discard()

remove an element from a set if it is a member (no-return)

my_set = {1,2,3,4,5,6}

my_set.discard(5)
print(my_set)   #Output: {1, 2, 3, 4, 6}

my_set.discard(10)
print(my_set)   #Output: {1, 2, 3, 4, 6}

difference_update()

removes all the elements of another set from this set

my_set = {1,2,3,4,5,6}
your_set = {4,5,6,7,8,9}

my_set.difference_update(your_set)
print(my_set)   #Output: {1, 2, 3}

difference_update()

removes all the elements of another set from this set

difference() and difference_update() methods do the same thing but difference returns the difference and difference_update updates the set.

my_set = {1,2,3,4,5,6}
your_set = {4,5,6,7,8,9}

my_set.difference_update(your_set)
print(my_set)   #Output: {1, 2, 3}

intersection()

returns a set, that is the intersection of two other sets (common elements among the sets)

my_set = {1,2,3,4,5,6}
your_set = {4,5,6,7,8,9}

print(my_set.intersection(your_set)) #Output: {4, 5, 6}

isdisjoint()

returns boolen value whether two sets have a intersection elements or not

my_set = {1,2,3,4,5,6}
your_set = {4,5,6,7,8,9}

print(my_set.isdisjoint(your_set)) #Output: False

my_set = {1,2,3}
your_set = {4,5,6,7,8,9}

print(my_set.isdisjoint(your_set)) #Output: True

union()

return a set containing the union of sets

my_set = {1,2,3,4,5,6}
your_set = {4,5,6,7,8,9}

print(my_set.union(your_set)) #Output: {1, 2, 3, 4, 5, 6, 7, 8, 9}

issubset()

returns boolean value whether another set contains this set or not

my_set = {4,5,6}
your_set = {4,5,6,7,8,9}

print(my_set.issubset(your_set)) #Output: True

my_set = {1,2,3}
your_set = {4,5,6,7,8,9}

print(my_set.issubset(your_set)) #Output: False

issuperset()

returns boolean value whether this set contains another set or not

my_set   = {4,5,6}
your_set = {4,5,6,7,8,9}

print(your_set.issuperset(my_set)) #Output: True

my_set   = {1,2,3}
your_set = {4,5,6,7,8,9}

print(your_set.issuperset(my_set)) #Output: False

symmetric_difference()

return a set of elements that are in either my_set or your_set, but not in their intersection

my_set   = {1,2,3,4,5,6}
your_set = {4,5,6,7,8,9}

print(my_set.symmetric_difference(your_set)) #Output: {1, 2, 3, 7, 8, 9}

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