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.
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)
Try it Yourself »
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)
Try it Yourself »
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)
Try it Yourself »
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))
Try it 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}
Try it Yourself »
A set can contain different data types:
Example
A set with strings, integers and boolean values:
set1 = {"abc", 34, True, 40, "male"}
Try 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))
Try 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)
Try it 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.