Python - Sets

Set

Sets are used to store multiple items in a single variable.

Set is one of 4 built-in data types in Python used to store collections of data, the other 3 are List, Tuple, and Dictionary, all with different qualities and usage.

A set is a collection which is unordered, unchangeable*, and unindexed.

💡 Note: Set items are unchangeable, but you can remove items and add new items.

Sets are written with curly brackets.

Create a Set:

thisset = {"apple", "banana", "cherry"}
print(thisset)

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

</aside>

Set Items

Set items are unordered, unchangeable, and do not allow duplicate values.

Unordered

Unordered means that the items in a set do not have a defined order.

Set items can appear in a different order every time you use them, and cannot be referred to by index or key.

Unchangeable

Set items are unchangeable, meaning that we cannot change the items after the set has been created.

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

Duplicates Not Allowed

Sets cannot have two items with the same value.

Get the Length of a Set

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

thisset = {"apple", "banana", "cherry", "banana"}
print(len(thisset))

Set Items - Data Types

Set items can be of any data type:

String, int and boolean data types:

set1 = {"apple", "banana", "cherry"}
set2 = {1, 5, 7, 9, 3}
set3 = {True, False, False}

A set with strings, integers and boolean values:

set1 = {"abc", 34, True, 40, "male"}

type()

From Python's perspective, sets are defined as objects with the data type 'set':

myset = {"apple", "banana", "cherry"}
print(type(myset))
# <class 'set'>

The set() Constructor

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

Using the set() constructor to make a set:

thisset = set(("apple", "banana", "cherry")) # note the double round-brackets
print(thisset)

Access Items

You cannot access items in a set by referring to an index or a key.

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.

thisset = {"apple", "banana", "cherry"}
for x in thisset:
print(x)

Check if "banana" is present in the set:

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

Change Items

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

Join Two Sets

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

You 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:

The union() method returns a new set with all items from both sets:

set1 = {"a", "b" , "c"}
set2 = {1, 2, 3}
set3 = set1.union(set2)
print(set3)

The update() method inserts the items in set2 into set1:

set1 = {"a", "b" , "c"}
set2 = {1, 2, 3}
set1.update(set2)
print(set1)

<aside> 💡 Note: Both union()and update() will exclude any duplicate items.

</aside>

Keep ONLY the Duplicates

The intersection_update() method will keep only the items that are present in both sets.

Keep the items that exist in both set x, and set y:

x = {"apple", "banana", "cherry"}
y = {"google", "microsoft", "apple"}
x.intersection_update(y)
print(x)

The intersection() method will return a new set, that only contains the items that are present in both sets.

Return a set that contains the items that exist in both set x, and set y:

x = {"apple", "banana", "cherry"}
y = {"google", "microsoft", "apple"}
z = x.intersection(y)
print(z)

Keep All, But NOT the Duplicates

The symmetric_difference_update() method will keep only the elements that are NOT present in both sets.

Keep the items that are not present in both sets:

x = {"apple", "banana", "cherry"}
y = {"google", "microsoft", "apple"}
x.symmetric_difference_update(y)
print(x)

The symmetric_difference() method will return a new set, that contains only the elements that are NOT present in both sets.

Return a set that contains all items from both sets, except items that are present in both:

x = {"apple", "banana", "cherry"}
y = {"google", "microsoft", "apple"}
z = x.symmetric_difference(y)
print(z)

Set Methods