Adding and removing set elements in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

How do you add a single element to a set in Python?

Use the add() method. For example, my_set.add(5) adds the element 5 to my_set.

beginner

What method removes an element from a set and raises an error if the element is not present?

The remove() method removes an element but raises a KeyError if the element is not found.

intermediate

What is the difference between discard() and remove() methods in sets?

discard() removes an element if it exists but does nothing if it doesn't. remove() raises an error if the element is missing.

beginner

How can you add multiple elements to a set at once?

Use the update() method with an iterable. For example, my_set.update([1, 2, 3]) adds 1, 2, and 3 to my_set.

beginner

What happens if you try to add a duplicate element to a set?

Nothing changes because sets only keep unique elements. Adding a duplicate does not add a new element.

Which method adds a single element to a set without error if the element already exists?

A pop()

B remove()

C discard()

D add()

The add() method adds an element and does nothing if it already exists, so no error occurs.

Which method removes an element from a set but does NOT raise an error if the element is missing?

A discard()

B remove()

C pop()

D clear()

discard() removes the element if present but does nothing if it is not, so no error is raised.

What will happen if you call remove() on an element not in the set?

A The element is added

B Nothing happens

C A KeyError is raised

D The set is cleared

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

How do you add multiple elements to a set at once?

A update() with an iterable

B remove() with multiple arguments

C add() with a list

D discard() with a list

update() takes an iterable and adds all its elements to the set.

If you add a duplicate element to a set, what happens?

A An error is raised

B The set ignores the duplicate

C The duplicate is added

D The set clears all elements

Sets only keep unique elements, so duplicates are ignored.

Explain how to add and remove elements from a Python set, including how to handle missing elements safely.

Think about methods that add one or many elements, and methods that remove with or without errors.

Describe what happens when you add duplicate elements to a set and why sets behave this way.

Consider the nature of sets as collections of unique items.