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Python Sets

Learn all about Python Sets in this comprehensive tutorial.

5 min read beginner
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  • •Sets are used to store multiple items in a single variable.
  • •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 are unchangeable, meaning that we cannot change the items after the set has been created.
  • •Sets cannot have two items with the same value.
  • •To determine how many items a set has, use the len() function.
  • •Set items can be of any data type:
  • •From Python's perspective, sets are defined as objects with the data type 'set':
  • •It is also possible to use the set() constructor to make a set.
  • •There are four collection data types in the Python programming language:

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

Sets are written with curly brackets.

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Note: 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

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.

Note: 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.

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Note: Note: The values True and 1 are considered the same value in sets, and are treated as duplicates:
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Note: Note: The values False and 0 are considered the same value in sets, and are treated as duplicates:
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Get the Length of a Set

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

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Set Items - Data Types

Set items can be of any data type:

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A set can contain different data types:

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type()

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

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The set() Constructor

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

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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.
Note: *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.

Module quiz

2 questions
1

Which of the following is true about Python Sets?

2

What is the most common pitfall when working with Python Sets?

Answer all questions to submit.

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Tuple Exercises
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Access Set Items