Comprehensive guide to Python set methods

In this article, we will explore the various methods available for Python sets, which are unordered collections of unique elements. Sets can be used for a wide range of tasks, such as removing duplicates, performing set operations like union, intersection, and difference, and testing membership and subsets. By mastering the set methods, you can enhance your Python skills and write more efficient and elegant code.

Creating and initializing sets

To create a set, you can use the curly braces {} notation or the built-in set() function. If you want to initialize a set with some elements, you can use the same syntax as for lists, tuples, or strings, but without duplicates. For example:

fruits = {'apple', 'banana', 'cherry'}
colors = set(['red', 'green', 'blue'])
vowels = set('aeiou')

Note that the order of the elements is arbitrary and may change between runs, as sets are implemented using hash tables.

Basic set operations

Once you have created some sets, you can perform various operations on them. The most common ones are:

• Union: combines the elements of two or more sets into a new set that contains all the unique elements.

A = {1, 2, 3}
B = {2, 3, 4}
C = {3, 4, 5}
print(A.union(B, C))

• Intersection: finds the common elements of two or more sets, i.e., the elements that belong to all of them.

A = {1, 2, 3}
B = {2, 3, 4}
C = {3, 4, 5}
print(A.intersection(B, C))

• Difference: removes the elements of one set from another set, i.e., the elements that belong only to the first set.

A = {1, 2, 3}
B = {2, 3, 4}

A.difference(B)

• Symmetric difference: finds the elements that belong to exactly one of two sets, i.e., the elements that are not common to both sets.

A = {1, 2, 3}
B = {2, 3, 4}

print(A.symmetric_difference(B))

• Subset and superset: check if one set is a subset or a superset of another set, i.e., if all the elements of the first set are also in the second set, or vice versa.

A = {1, 2, 3}
B = {2, 3, 4}
C = {3, 4, 5}
print(A.issubset(B))
# False
print(A.issubset(A.union(B)))
# True
print(A.issuperset(B))
# False
print(A.union(B).issuperset(A))
# True

Modifying sets

Sets are mutable objects, meaning that you can add or remove elements from them, or update them with the elements of other sets. The most common methods for modifying sets are:

• Add: inserts a new element into the set, if it is not already present.

A = {1, 2, 3}

A.add(0)
print(A)

• Remove: removes an element from the set, raising a KeyError if it is not present.

A = {0, 1, 2, 3}

A.remove(0)
print(A)

• Discard: removes an element from the set, without raising an error if it is not present.

A = {0, 1, 2, 3}
A.discard(0)
print(A)

• Pop: removes and returns an arbitrary element from the set, raising a KeyError if it is empty.

A = {1, 2, 3}

A.pop()
print(A)

• Update: adds the elements of one or more sets into the set, ignoring duplicates.

A = {1, 2, 3}
B = {2, 3, 4}
A.update(B)
print(A)

• Clear: removes all the elements from the set, making it empty.

A = {1, 2, 3}
A.clear()
print(A)

Set methods summary

Here is a summary of the set methods we have covered in this article: