Sets

What is a set?

A Set is a collection that is unordered, unindexed, and—most importantly contains no duplicate members.

Think of a set like a physical bag of labeled marbles. You can reach in and grab one, but they aren't sitting in a neat line (unordered), and you can’t have two marbles that are exactly the same.

Set Syntax

Sets are written with curly braces {}, just like dictionaries, but they don't have "keys" or "colon pairs." They just have items.

• Print my_set.
• Print numbers.

Basic Set Methods

Since you can't use an index to change an item, you use these methods to manage the items in your set:

• .add(): Adds an item to the set.
• .remove(): Removes a specific item (raises an error if the item is not found).
• .discard(): Removes an item (does not raise an error if the item is missing).
• .clear(): Empties the entire set.

1. Print skills.
2. Remove HTML from skills and print again.
3. Discard C++ from skills and print again.
4. Clear skills and print.

Because sets are unordered, we cannot find data using slicing. However, we can use the in keyword to see if a specific value is in the set.

• Print C++ in skills.

One last caveat: because sets only store unique values, if we have a set nums = {2, 3, 3, 4, 4, 4, 6, 6, 6, 6, 6, 6} and we check the length using len(nums), we get 4, not 12. This is because Python ignores all those duplicate entries.

Scenario: Removing Duplicates

We can use the set() function to return a set with no duplicates from a list that has repeated items:

• print unique_items.

Exercise 1: Set Creation

• Task: Create a set named coding_languages containing "Python", "JavaScript", and "C++".
• Goal: Print the set and notice that the order of items is not the same as how you typed them.

Exercise 2: Adding and Removing

• Task: Create a set fruits = {"apple", "banana"}.
• Goal: Add "orange" using .add() and remove "apple" using .remove(). Print the final set.

Exercise 3: Membership Testing

• Task: Create a set prime_numbers = {2, 3, 5, 7, 11}.
• Goal: Use the in keyword to check if 5 is in the set and print the result (True/False).

Exercise 4: The Length Caveat

• Task: Create a set test_scores = {90, 85, 90, 70, 85, 100}.
• Goal: Use len() to find the length of the set and print it. Observe why the number is smaller than the items typed.

Exercise 5: Instant Deduplication

• Task: Create a list names = ["Sarah", "John", "Sarah", "Pete", "John"].
• Goal: Convert this list into a set to remove duplicates, then convert it back into a list. Print the final list.