A set is an unordered collection of items. Every element is unique (no duplicates) and must be immutable (which cannot be changed).
However, the set itself is mutable. We can add or remove items from it.
Sets can be used to perform mathematical set operations like union, intersection, symmetric difference etc.
A set is created by placing all the items (elements) inside curly braces {}, separated by comma or by using the built-in function set().
It can have any number of items and they may be of different types (integer, float, tuple, string etc.). But a set cannot have a mutable element, like list, set or dictionary, as its element.
>>> # set of integers
>>> my_set = {1, 2, 3}
>>> print(my_set)
{1, 2, 3}
>>> my_set = {1.0, "Hello", (1, 2, 3)}
>>> print(my_set)
{1.0, (1, 2, 3), 'Hello'}
>>> Sets are a powerful tool in Python since they have the ability to calculate differences and intersections between other sets. For example, say you have a list of participants in events A and B :
>>> a = set(["chanti", "Ramana", "Venkat"])
>>> print(a)
{'chanti', 'Ramana', 'Venkat'}
>>> b = set(["Ramana", "Reddy"])
>>> print(b)
{'Reddy', 'Ramana'}
>>> A particular item can be removed from set using methods, discard() and remove().
The only difference between the two is that, while using discard() if the item does not exist in the set, it remains unchanged. But remove() will raise an error in such condition.
>>> # initialize my_set
>>> my_set = {1, 2, 3, 4, 5, 6, 7}
>>> print(my_set)
{1, 2, 3, 4, 5, 6, 7}
>>> my_set.discard(6)
>>> print(my_set)
{1, 2, 3, 4, 5, 7}
>>> my_set.remove(2)
>>> print(my_set)
{1, 3, 4, 5, 7}
>>> my_set.discard(2)
>>> print(my_set)
{1, 3, 4, 5, 7}There are many set methods, some of which we have already used above. Here is a list of all the methods that are available with set objects.
| Method | Description |
|---|---|
| add() | Add an element to a set |
| update() | Update a set with the union of itself and others |
| remove() | Remove an element from a set. If the element is not a member, raise a KeyError |
| copy() | Return a shallow copy of a set |
| difference() | Return the difference of two or more sets as a new set |
| difference_update() | Remove all elements of another set from this set |
| discard() | Remove an element from set if it is a member. (Do nothing if the element is not in set) |
| clear() | Remove all elements form a set |
| intersection() | Return the intersection of two sets as a new set |
| intersection_update() | Update the set with the intersection of itself and another |
| isdisjoint() | Return True if two sets have a null intersection |
| issubset() | Return True if another set contains this set |
| issuperset() | Return True if this set contains another set |
| pop() | Remove and return an arbitary set element. Raise KeyError if the set is empty |
| symmetric_difference() | Return the symmetric difference of two sets as a new set |
| symmetric_difference_update() | Update a set with the symmetric difference of itself and another |
| union() | Return the union of sets in a new set |