Python Sets
myset = {"apple", "banana", "cherry"}
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.
Example
Create a Set:
thisset = {"apple", "banana", "cherry"}
print(thisset)
Try it Yourself
»
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.
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.
Example
Duplicate values will be ignored:
thisset = {"apple", "banana", "cherry", "apple"}
print(thisset)
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Note: The values True
and 1 are considered the same value in sets,
and are treated as duplicates:
Example
True
and 1 is considered the same value:
thisset = {"apple", "banana", "cherry", True, 1, 2}
print(thisset)
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Note: The values False
and 0 are considered the same value in sets,
and are treated as duplicates:
Example
False
and 0 is considered the same value:
thisset = {"apple", "banana", "cherry", False, True, 0}
print(thisset)
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Get the Length of a Set
To determine how many items a set has, use the len()
function.
Example
Get the number of items in a set:
thisset = {"apple", "banana", "cherry"}
print(len(thisset))
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Yourself »
Set Items - Data Types
Set items can be of any data type:
Example
String, int and boolean data types:
set1 = {"apple", "banana", "cherry"}
set2 = {1, 5, 7, 9, 3}
set3 = {True, False, False}
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it Yourself »
A set can contain different data types:
Example
A set with strings, integers and boolean values:
set1 = {"abc", 34, True, 40, "male"}
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it Yourself »
type()
From Python's perspective, sets are defined as objects with the data type 'set':
<class 'set'>
Example
What is the data type of a set?
myset = {"apple", "banana", "cherry"}
print(type(myset))
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it Yourself »
The set() Constructor
It is also possible to use the set()
constructor to make a set.
Example
Using the set() constructor to make a set:
thisset = set(("apple", "banana", "cherry")) # note the double round-brackets
print(thisset)
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Yourself »
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.