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"}
print(thisset)
Note: Sets are unordered, so you cannot be sure in which order the items will appear.
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.
Sets cannot have two items with the same value.
Duplicate values will be ignored:
thisset = {"apple", "banana", "cherry", "apple"}
print(thisset)
To determine how many items a set has, use the len()
function.
Get the number of items in a set:
thisset = {"apple", "banana", "cherry"}
print(len(thisset))
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 can contain different data types:
A set with strings, integers and boolean values:
set1 = {"abc", 34, True, 40, "male"}
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"}
print(type(myset))
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)
There are four collection data types in the Python programming language:
*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.
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.
Loop through the set, and print the values:
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)
Once a set is created, you cannot change its items, but you can add new items.
Once a set is created, you cannot change its items, but you can add new items.
To add one item to a set use the add()
method.
Add an item to a set, using the add()
method:
thisset = {"apple", "banana", "cherry"}
thisset.add("orange")
print(thisset)
To add items from another set into the current set, use the update()
method.
Add elements from tropical into
thisset:
thisset = {"apple", "banana", "cherry"}
tropical = {"pineapple", "mango", "papaya"}
thisset.update(tropical)
print(thisset)
The object in the update() method does not have
to be a set, it can be any iterable object (tuples, lists, dictionaries etc.).
Add elements of a list to at set:
thisset = {"apple", "banana", "cherry"}
mylist = ["kiwi", "orange"]
thisset.update(mylist)
print(thisset)
To remove an item in a set, use the remove(), or the discard() method.
Remove "banana" by using the remove()
method:
thisset = {"apple", "banana", "cherry"}
thisset.remove("banana")
print(thisset)
Note: If the item to remove does not exist, remove() will raise an error.
Remove "banana" by using the discard()
method:
thisset = {"apple", "banana", "cherry"}
thisset.discard("banana")
print(thisset)
Note: If the item to remove does not exist, discard() will
NOT raise an error.
You can also use the pop() method to remove
an item, but this method will remove the last item. Remember that sets
are unordered, so you will not know what item that gets removed.
The return value of the pop() method is the
removed item.
Remove the last item by using the pop()
method:
thisset = {"apple", "banana", "cherry"}
x =
thisset.pop()
print(x)
print(thisset)
Note: Sets are unordered, so when using the pop() method,
you do not know which item that gets removed.
The clear()
method empties the set:
thisset = {"apple", "banana", "cherry"}
thisset.clear()
print(thisset)
The del keyword will delete the set
completely:
thisset = {"apple", &qquot;banana", "cherry"}
del
thisset
print(thisset)
You can loop through the set items by using a for
loop:
Loop through the set, and print the values:
thisset = {"apple", "banana", "cherry"}
for x in thisset:
print(x)
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)
Note: Both union() and update()
will exclude any duplicate items.
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)
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)
Python has a set of built-in methods that you can use on sets.
| Method | Description |
|---|---|
| add() | Adds an element to the set |
| clear() | Removes all the elements from the set |
| copy() | Returns a copy of the set |
| difference() | Returns a set containing the difference between two or more sets |
| difference_update() | Removes the items in this set that are also included in another, specified set |
| discard() | Remove the specified item |
| intersection() | Returns a set, that is the intersection of two other sets |
| intersection_update() | Removes the items in this set that are not present in other, specified set(s) |
| isdisjoint() | Returns whether two sets have a intersection or not |
| issubset() | Returns whether another set contains this set or not |
| issuperset() | Returns whether this set contains another set or not |
| pop() | Removes an element from the set |
| remove() | Removes the specified element |
| symmetric_difference() | Returns a set with the symmetric differences of two sets |
| symmetric_difference_update() | inserts the symmetric differences from this set and another |
| union() | Return a set containing the union of sets |
| update() | Update the set with the union of this set and others |