CyberStars

Sets

We know lists, tuples, and dictionaries. Time for the last big collection type: sets

A set is a collection where every element is unique. No duplicates allowed. Think of it like a guest list for a party: each person can only be on the list once

guests = {"Tommy", "Lance", "Cortez", "Tommy"}
print(guests)

Output

{'Lance', 'Cortez', 'Tommy'}

Wait, we wrote Tommy twice, but he only appears once. That's the whole point of a set: it automatically removes duplicates. Also notice that the order might be different from how we wrote them. Sets don't care about order, only about what's inside

Sets use curly braces {}, just like dictionaries. But there's no key: value, just values. If it has colons it's a dictionary, if it doesn't it's a set

my_set = {1, 2, 3}
my_dict = {"a": 1, "b": 2}

Be careful with empty collections

empty_dict = {}
empty_set = set()

An empty {} creates a dictionary, not a set. To create an empty set, use set()

We can add elements with .add() and remove them with .remove()

weapons = {"bat", "pistol"}
weapons.add("shotgun")
print(weapons)

weapons.remove("bat")
print(weapons)

Notice we use .add(), not .append() like with lists. Sets don't have an order, so "appending at the end" doesn't make sense

The most useful thing about sets: checking if something is in the set. This is extremely fast, much faster than checking in a list

banned_players = {"Sonny", "Diaz", "Gonzalez"}

player = "Tommy"
if player in banned_players:
    print(f"{player} is banned!")
else:
    print(f"{player} is welcome")

Output Tommy is welcome

A super common use case: removing duplicates from a list

names = ["Tommy", "Lance", "Tommy", "Cortez", "Lance", "Lance"]
unique_names = list(set(names))
print(unique_names)

We converted the list to a set (which removed duplicates), then back to a list. Clean and simple

len() works on sets too

colors = {"red", "green", "blue", "red"}
print(len(colors))

Output 3, not 4, because the duplicate red was removed

Mission: Signal Log

The station picked up a list of signal codes, stored in a variable named signals, and many repeat. Do the following:

  1. Print Total: then the total number of signals (length of the list)
  2. Make a set of the unique codes
  3. Print Unique: then how many unique codes there are
  4. Check whether the code D4 was picked up: print D4 detected if it is in the set, otherwise D4 missing

Output

Total: 8
Unique: 4
D4 detected