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Python Sets

myset = {"apple", "banana", "cherry"}


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

Set Items

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


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.


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.


Duplicate values will be ignored:

thisset = {"apple", "banana", "cherry", "apple"}

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Note: The values True and 1 are considered the same value in sets, and are treated as duplicates:


True and 1 is considered the same value:

thisset = {"apple", "banana", "cherry", True, 1, 2}

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Get the Length of a Set

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


Get the number of items in a set:

thisset = {"apple", "banana", "cherry"}

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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}
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A set can contain different data types:


A set with strings, integers and boolean values:

set1 = {"abc", 34, True, 40, "male"}
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From Python's perspective, sets are defined as objects with the data type 'set':

<class 'set'>


What is the data type of a set?

myset = {"apple", "banana", "cherry"}
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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
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Python Collections (Arrays)

There are four collection data types in the Python programming language:

  • List is a collection which is ordered and changeable. Allows duplicate members.
  • Tuple is a collection which is ordered and unchangeable. Allows duplicate members.
  • Set is a collection which is unordered, unchangeable*, and unindexed. No duplicate members.
  • Dictionary is a collection which is ordered** and changeable. No duplicate members.

*Set items are unchangeable, but you can remove items and add new items.

**As of Python version 3.7, dictionaries are ordered. In Python 3.6 and earlier, dictionaries are unordered.

When choosing a collection type, it is useful to understand the properties of that type. Choosing the right type for a particular data set could mean retention of meaning, and, it could mean an increase in efficiency or security.