Remove Elements From a Set in Python

We use sets in python to store unique immutable objects. In this article, we will discuss how we can remove elements from a set in python. For this, we will discuss four approaches using different methods.

Remove Elements From a Set Using The pop() Method

We can use the pop() method to remove elements from a set. The pop() method, when invoked on a set, accepts no input argument. After execution, it removes a random element from the set and returns the element. You can observe this in the following example.

mySet = {1, 2, 3, 4, 5, 6}
print("The input set is:", mySet)
element = mySet.pop()
print("The output set is:", mySet)
print("The popped element is:", element)

Output:

The input set is: {1, 2, 3, 4, 5, 6}
The output set is: {2, 3, 4, 5, 6}
The popped element is: 1

The pop() method works well only on sets that are not empty. If we invoke the pop() method on an empty set, it will raise the KeyError exception as shown below.

mySet = set()
print("The input set is:", mySet)
element = mySet.pop()
print("The output set is:", mySet)
print("The popped element is:", element)

Output:

The input set is: set()
/usr/lib/python3/dist-packages/requests/__init__.py:89: RequestsDependencyWarning: urllib3 (1.26.7) or chardet (3.0.4) doesn't match a supported version!
  warnings.warn("urllib3 ({}) or chardet ({}) doesn't match a supported "
Traceback (most recent call last):
  File "/home/aditya1117/PycharmProjects/pythonProject/string1.py", line 3, in <module>
    element = mySet.pop()
KeyError: 'pop from an empty set'

The pop() method removes a random element from the set. If we have to remove a specific element, we can use the approaches discussed below.

Remove Elements From a Set Using The remove() Method

To remove a specified element from a set, we can use the remove() method. The remove() method, when invoked on a set, takes an element as an input argument and removes the element from the set as shown below.  

mySet = {1, 2, 3, 4, 5, 6}
print("The input set is:", mySet)
mySet.remove(3)
print("The output set is:", mySet)

Output:

The input set is: {1, 2, 3, 4, 5, 6}
The output set is: {1, 2, 4, 5, 6}

If the element passed as the input to the remove() method isn’t present in the set, the program will run into a KeyError exception as shown below.

mySet = {1, 2, 3, 4, 5, 6}
print("The input set is:", mySet)
mySet.remove(7)
print("The output set is:", mySet)

Output:

The input set is: {1, 2, 3, 4, 5, 6}
/usr/lib/python3/dist-packages/requests/__init__.py:89: RequestsDependencyWarning: urllib3 (1.26.7) or chardet (3.0.4) doesn't match a supported version!
  warnings.warn("urllib3 ({}) or chardet ({}) doesn't match a supported "
Traceback (most recent call last):
  File "/home/aditya1117/PycharmProjects/pythonProject/string1.py", line 3, in <module>
    mySet.remove(7)
KeyError: 7

Similarly, if we try to remove an element from an empty set using the remove() method, it will raise the KeyError exception.

mySet = set()
print("The input set is:", mySet)
mySet.remove(7)
print("The output set is:", mySet)

Output:

The input set is: set()
/usr/lib/python3/dist-packages/requests/__init__.py:89: RequestsDependencyWarning: urllib3 (1.26.7) or chardet (3.0.4) doesn't match a supported version!
  warnings.warn("urllib3 ({}) or chardet ({}) doesn't match a supported "
Traceback (most recent call last):
  File "/home/aditya1117/PycharmProjects/pythonProject/string1.py", line 3, in <module>
    mySet.remove(7)
KeyError: 7

Remove Elements From a Set Using The discard() Method

When we try to remove an element from a set using the remove() method, and the element is not present in the set, the program will run into a KeyError exception. You can avoid this using the discard() method instead of the remove() method. The discard() method, when invoked on a set, accepts an element as the input argument and removes the element from the set as in the case of the remove() method.

mySet = {1, 2, 3, 4, 5, 6}
print("The input set is:", mySet)
mySet.discard(3)
print("The output set is:", mySet)

Output:

The input set is: {1, 2, 3, 4, 5, 6}
The output set is: {1, 2, 4, 5, 6}

However, the discard() method does not raise an exception if we try to remove an element that isn’t already present in the set. The set remains unchanged and the program doesn’t run into the KeyError exception.

mySet = {1, 2, 3, 4, 5, 6}
print("The input set is:", mySet)
mySet.discard(7)
print("The output set is:", mySet)

Output:

The input set is: {1, 2, 3, 4, 5, 6}
The output set is: {1, 2, 3, 4, 5, 6}

Using The clear() Method

The clear() method is used to remove all the elements from any given set at once. When invoked on a set, the clear() method takes no input arguments and removes all the elements from the set. You can observe this in the following example.

mySet = {1, 2, 3, 4, 5, 6}
print("The input set is:", mySet)
mySet.clear()
print("The output set is:", mySet)

Output:

The input set is: {1, 2, 3, 4, 5, 6}
The output set is: set()

Conclusion

In this article, we have discussed four ways to remove elements from a set in python. To know more about sets, you can read this article on set comprehension in Python. You might also like this article on list comprehension in Python.