Adding and removing set elements in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code adding elements to a set?

Consider the following Python code that adds elements to a set. What will be printed?

Python

s = {1, 2, 3}
s.add(4)
s.add(2)
print(s)

A {1, 2, 3, 4}

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

C {4}

D Error: cannot add duplicate elements

💡 Hint

Remember that sets do not allow duplicates.

Adding 4 to the set adds a new element. Adding 2 again does nothing because 2 is already in the set. So the set contains {1, 2, 3, 4}.

❓ Predict Output

intermediate

What happens when removing an element not in the set?

What will happen when this code runs?

Python

s = {10, 20, 30}
s.remove(40)
print(s)

A KeyError

B {10, 20, 30}

C None

D Set unchanged: {10, 20, 30}

💡 Hint

Check what remove() does if the element is missing.

The remove() method raises a KeyError if the element is not found in the set.

❓ Predict Output

advanced

What is the output after using discard on a set?

Look at this code and decide what it prints.

Python

s = {5, 6, 7}
s.discard(6)
s.discard(10)
print(s)

A {5, 6, 7}

B {5, 6, 7, 10}

C KeyError

D {5, 7}

💡 Hint

Discard does not raise an error if the element is missing.

Discard removes 6 from the set. Discarding 10 does nothing because 10 is not in the set and no error is raised.

🧠 Conceptual

advanced

Which method safely removes an element without error if missing?

You want to remove an element from a set but avoid errors if it is not present. Which method should you use?

A remove()

B discard()

C pop()

D clear()

💡 Hint

One method raises an error if the element is missing, the other does not.

discard() removes the element if present but does nothing if missing, so it is safe to use.

❓ Predict Output

expert

What is the final set after these operations?

Analyze the code below and determine the final content of the set.

Python

s = set()
s.add(1)
s.add(2)
s.add(3)
s.remove(2)
s.discard(4)
s.add(2)
s.remove(1)
print(s)

A {3}

B {1, 2, 3, 4}

C {2, 3}

D {1, 3}

💡 Hint

Track each add and remove step carefully.

Initially empty set. Add 1,2,3 → {1,2,3}. Remove 2 → {1,3}. Discard 4 (no error) → {1,3}. Add 2 → {1,2,3}. Remove 1 → {2,3}.