As you can see, we wrote it in the order 1, 3, 2. In point b, we will access this set and see what we get back.<\/p>\n
A set may contain values of different types.<\/p>\n
>>> c={1,2.0,'three'}<\/pre>\na. Duplicate Elements<\/strong><\/p>\nA set also cannot contain duplicate elements. Let\u2019s try adding duplicate elements to another set, and then access it in point b.<\/p>\n
>>> b={3,2,1,2}<\/pre>\nb. Mutability<\/strong><\/p>\nA set is mutable, but may not contain mutable items like a list, set, or even a dictionary.<\/p>\n
>>> d={[1,2,3],4}<\/pre>\nOutput<\/strong><\/p>\n\nTraceback (most recent call last):File “<pyshell#9>”, line 1, in <module>d={[1,2,3],4}<\/p>\n
TypeError: unhashable type: ‘list’<\/p>\n<\/div>\n
As we discussed, there is no such thing as a nested Python set.<\/p>\n
>>> d={{1,3,2},4}<\/pre>\nOutput<\/strong><\/p>\n\nTraceback (most recent call last):File “<pyshell#10>”, line 1, in <module><\/p>\n
d={{1,3,2},4}<\/p>\n
TypeError: unhashable type: ‘set’<\/p>\n
c. The Python set() function<\/strong><\/p>\n<\/div>\nYou can also create a set with the set() function.<\/p>\n
>>> d=set()\r\n>>> type(d)<\/pre>\nOutput<\/strong><\/p>\n<class \u2018set\u2019><\/div>\nThis creates an empty set object. Remember that if you declare an empty set as the following code, it is an empty dictionary, not an empty set. We confirm this using the type() function.<\/p>\n
>>> d={}\r\n>>> type(d)<\/pre>\nOutput<\/strong><\/p>\n<class ‘dict’><\/div>\nThe set() function may also take one argument, however. It should be an iterable, like a list.<\/p>\n
>>> d=set([1,3,2])<\/pre>\n2. Accessing a Set in Python<\/h4>\n
Since sets in Python do not support indexing, it is only possible to access the entire set at once. Let\u2019s try accessing the sets from point a.<\/p>\n
>>> a<\/pre>\nOutput<\/strong><\/p>\n{1, 2, 3}<\/div>\nDid you see how it reordered the elements into an ascending order? Now let\u2019s try accessing the set c.<\/p>\n
>>> c<\/pre>\nOutput<\/strong><\/p>\n{1, 2.0, ‘three’}<\/div>\nFinally, let\u2019s access set b.<\/p>\n
>>> b<\/pre>\nOutput<\/strong><\/p>\n{1, 2, 3}<\/div>\nAs you can see, we had two 2s when we declared the set, but now we have only one, and it automatically reordered the set.<\/p>\n
Also, since sets do not support indexing, they cannot be sliced. Let\u2019s try slicing one.<\/p>\n
>>> b[1:]<\/pre>\nOutput<\/strong><\/p>\n\nTraceback (most recent call last):File “<pyshell#26>”, line 1, in <module><\/p>\n
b[1:]<\/p>\n
TypeError: ‘set’ object is not subscriptable<\/p>\n<\/div>\n
As you can see in the error, a set object is not subscriptable.<\/p>\n
3. Deleting a Set in Python<\/h4>\n
Again, because a set isn\u2019t indexed, you can\u2019t delete an element using its index. So for this, you must use one of the following methods.<\/p>\n
A method must be called on a set, and it may alter the set. For the following examples, let\u2019s take a set called numbers.<\/p>\n
>>> numbers={3,2,1,4,6,5}\r\n>>> numbers<\/pre>\nOutput<\/strong><\/p>\n{1, 2, 3, 4, 5, 6}<\/div>\na. discard() method in Python<\/strong><\/p>\nThis method takes the item to delete as an argument.<\/p>\n
>>> numbers.discard(3)\r\n>>> numbers<\/pre>\nOutput<\/strong><\/p>\n{1, 2, 4, 5, 6}<\/div>\nAs you can see in the resulting set, item 3 has been removed.<\/p>\n
b. remove() method in Python<\/strong><\/p>\nLike the discard() method, remove() deletes an item from the set.<\/p>\n
>>> numbers.remove(5)\r\n>>> numbers<\/pre>\nOutput<\/strong><\/p>\n{1, 2, 4, 6}<\/div>\ndiscard() vs remove():<\/strong><\/p>\nThese two methods may appear the same to you, but there\u2019s actually a difference.<\/p>\n
If you try deleting an item that doesn\u2019t exist in the set, discard() ignores it, but remove() raises a KeyError.<\/p>\n
>>> numbers.discard(7)\r\n>>> numbers<\/pre>\nOutput<\/strong><\/p>\n{1, 2, 4, 6}<\/div>\n>>> numbers.remove(7)<\/pre>\nOutput<\/strong><\/p>\n\nTraceback (most recent call last):File “<pyshell#37>”, line 1, in <module><\/p>\n
numbers.remove(7)<\/p>\n
KeyError: 7<\/p>\n<\/div>\n
c. pop() method in Python set<\/strong><\/p>\nLike in a dictionary, you can call the pop() method on a set. However, here, it does not take an argument.<\/p>\n
Because a set doesn\u2019t support indexing, there is absolutely no way to pass an index to the pop method. Hence, it pops out an arbitrary item.<\/p>\n
Furthermore, it prints out the item that was popped.<\/p>\n
>>> numbers.pop()<\/pre>\nOutput<\/strong><\/p>\n1<\/div>\nLet\u2019s try popping anot\/her element.<\/p>\n
>>> numbers.pop()<\/pre>\nOutput<\/strong><\/p>\n2<\/div>\nLet\u2019s try it on another set as well.<\/p>\n
>>> {2,1,3}.pop()<\/pre>\nOutput<\/strong><\/p>\n1<\/div>\nd. clear() method in Python set<\/strong><\/p>\nLike the pop method(), the clear() method for a dictionary can be applied to a Python set as well. It empties the set in Python.<\/p>\n
>>> numbers.clear()\r\n>>> numbers<\/pre>\nOutput<\/strong><\/p>\nset()<\/div>\nAs you can see, it denoted an empty set as set(), not as {}.<\/p>\n
4. Updating a Set in Python<\/h4>\n
As we discussed, a Python set is mutable. But as we have seen earlier, we can\u2019t use indices to reassign it.<\/p>\n
>>> numbers={3,1,2,4,6,5}\r\n>>> numbers[3]<\/pre>\nOutput<\/strong><\/p>\n\nTraceback (most recent call last):File “<pyshell#56>”, line 1, in <module><\/p>\n
numbers[3]<\/p>\n
TypeError: ‘set’ object does not support indexing<\/p>\n<\/div>\n
So, we use two methods for this purpose- add() and update(). We have seen the update() method on tuples, lists, and strings.<\/p>\n
a. add() method in Python set<\/strong><\/p>\nIt takes as an argument the item to be added to the set.<\/p>\n
>>> numbers.add(3.5)\r\n>>> numbers<\/pre>\nOutput<\/strong><\/p>\n{1, 2, 3, 4, 5, 6, 3.5}<\/div>\nIf you add an existing item in the set, the set remains unaffected.<\/p>\n
>>> numbers.add(4)\r\n>>> numbers<\/pre>\nOutput<\/strong><\/p>\n{1, 2, 3, 4, 5, 6, 3.5}<\/div>\nb. update() method in Python set<\/strong><\/p>\nThis method can add multiple items to the set at once, which it takes as arguments.<\/p>\n
>>> numbers.update([7,8],{1,2,9})\r\n>>> numbers<\/pre>\nOutput<\/strong><\/p>\n{1, 2, 3, 4, 5, 6, 3.5, 7, 8, 9}<\/div>\nAs is visible, we could provide a list and a set as arguments to this. This is because this is different than creating a set.<\/p>\n
5. Python Functions on Sets<\/h4>\n
A function is something that you can apply to a Python set, and it performs operations on it and returns a value. Let\u2019s talk about some of the functions that a set supports.<\/p>\n
We\u2019ll take a new set for exemplary purposes.<\/p>\n
>>> days={'Monday','Tuesday','Wednesday','Thursday','Friday','Saturday','Sunday'}<\/pre>\na. len() function in Python set<\/strong><\/p>\nThe len() function returns the length of a set. This is the number of elements in it.<\/p>\n
>>> len(days)<\/pre>\nOutput<\/strong><\/p>\n7<\/div>\nb. max() function in Python set<\/strong><\/p>\nThis function returns the item from the set with the highest value.<\/p>\n
>>> max({3,1,2})<\/pre>\nOutput<\/strong><\/p>\n3<\/div>\nWe can make such a comparison on strings as well.<\/p>\n
>>> max(days)<\/pre>\nOutput<\/strong><\/p>\n‘Wednesday’<\/div>\nThe Python function returned \u2018Wednesday\u2019 because W has the highest ASCII value among M, T, W, F, and S.<\/p>\n
But we cannot compare values of different types.<\/p>\n
>>> max({1,2,'three','Three'})<\/pre>\nOutput<\/strong><\/p>\n\nTraceback (most recent call last):File “<pyshell#69>”, line 1, in <module><\/p>\n
max({1,2,’three’,’Three’})<\/p>\n
TypeError: ‘>’ not supported between instances of ‘str’ and ‘int’<\/p>\n<\/div>\n
c. min() function in Python set<\/strong><\/p>\nLike the max() function, the min() function returns the item in the Python set with the lowest value.<\/p>\n
>>> min(days)<\/pre>\nOutput<\/strong><\/p>\n‘Friday’<\/div>\nThis is because F has the lowest ASCII value among M, T, W, F, and S.<\/p>\n
d. sum() function in Python set<\/strong><\/p>\nThe sum() functionin Python set returns the arithmetic sum of all the items in a set.<\/p>\n
>>> sum({1,2,3})<\/pre>\nOutput<\/strong><\/p>\n6<\/div>\nHowever, you can\u2019t apply it to a set that contains strings.<\/p>\n
>>> sum(days)<\/pre>\nOutput<\/strong><\/p>\n\nTraceback (most recent call last):File “<pyshell#72>”, line 1, in <module><\/p>\n
sum(days)<\/p>\n
TypeError: unsupported operand type(s) for +: ‘int’ and ‘str’<\/p>\n<\/div>\n
e. any() function in Python set<\/strong><\/p>\nThis function returns True even if one item in the set has a Boolean value of True.<\/p>\n
>>> any({0})<\/pre>\nOutput<\/strong><\/p>\nFalse<\/div>\n>>> any({0,'0'})<\/pre>\nOutput<\/strong><\/p>\nTrue<\/div>\nIt returns True because the string \u20180\u2019 has a Boolean value of True.<\/p>\n
f. all() function in Python set<\/strong><\/p>\nUnlike the any() function, all() returns True only if all items in the Python set have a Boolean value of True. Otherwise, it returns False.<\/p>\n
>>> all({0,'0'})<\/pre>\nOutput<\/strong><\/p>\nFalse<\/div>\n>>> all(days)<\/pre>\nOutput<\/strong><\/p>\nTrue<\/div>\ng. sorted() function in Python set<\/strong><\/p>\nThe sorted() function returns a sorted python set to list. It is sorted in ascending order, but it doesn\u2019t modify the original set.<\/p>\n
>>> numbers={1, 2, 3, 4, 5, 6, 3.5}\r\n>>> sorted(numbers)<\/pre>\nOutput<\/strong><\/p>\n[1, 2, 3, 3.5, 4, 5, 6]<\/div>\n6. Python Methods on Sets<\/h4>\n
Unlike a function in Python set, a method may alter a set. It performs a sequence on operations on a set, and must be called on it.<\/p>\n
So far, we have learned about the methods add(), clear(), discard(), pop(), remove(), and update(). Now, we will see more methods from a more mathematical point of view.<\/p>\n
a. union() method in Python set<\/strong><\/p>\nThis method performs the union operation on two or more Python sets. What it does is it returns all the items that are in any of those sets.<\/p>\n
![\"Python](\"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2018\/01\/Pythin-union.jpg\")
<\/a>Union in Python Set<\/p><\/div>\n
>>> set1,set2,set3={1,2,3},{3,4,5},{5,6,7}\r\n>>> set1.union(set2,set3)<\/pre>\nOutput<\/strong><\/p>\n{1, 2, 3, 4, 5, 6, 7}<\/div>\n>>> set1\r\n<\/pre>\nOutput<\/strong><\/p>\n{1, 2, 3}<\/div>\nAs you can see, it did not alter set1. A method does not always alter a set in Python.<\/p>\n
b. intersection() method in Python set<\/strong><\/p>\nThis method takes as arguments sets, and returns the common items in all the sets.<\/p>\n
![\"Python](\"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2018\/01\/Python-intersection.jpg\")
<\/a>Intersection Set in Python<\/p><\/div>\n
>>> set2.intersection(set1)<\/pre>\nOutput<\/strong><\/p>\n{3}<\/div>\nLet\u2019s intersect all three sets.<\/p>\n
>>> set2.intersection(set1,set3)<\/pre>\nOutput<\/strong><\/p>\nset()<\/div>\nIt returned an empty set because these three sets have nothing in common.<\/p>\n
c. difference() method in Python set<\/strong><\/p>\nThe difference() method returns the difference of two or more sets. It returns as a set.<\/p>\n