Using Sets in Your Code

The idea

You know what a set is and why it exists.

Now let's look at what you can actually do with one — adding, removing, checking, and comparing.

Adding and removing elements

add() adds one element. If it already exists — nothing happens.

squad = {"Raven", "Wolf", "Ghost"}
squad.add("Viper")
squad.add("Raven")      # already there — ignored
print(squad)

Output → {'Ghost', 'Raven', 'Viper', 'Wolf'}

remove() removes an element — raises KeyError if not found.

discard() removes an element — silently does nothing if not found.

squad.remove("Wolf")        # KeyError if missing
squad.discard("Fox")        # no error if missing

pop() removes and returns a random element — sets are unordered, so you don't control which one.

removed = squad.pop()
print(removed)              # unpredictable — could be any element

clear() empties the set.

Checking membership

in works the same as with lists — but faster:

squad = {"Raven", "Wolf", "Ghost"}
print("Wolf" in squad)      # True
print("Fox" in squad)       # False

Set operations — where sets shine

Sets support mathematical operations that lists don't.

Union — all elements from both sets, no duplicates:

alpha = {"Raven", "Wolf", "Ghost"}
bravo = {"Ghost", "Viper", "Bull"}
print(alpha | bravo)

Output → {'Bull', 'Ghost', 'Raven', 'Viper', 'Wolf'}

Intersection — only elements that appear in both:

print(alpha & bravo)

Output → {'Ghost'}

Difference — elements in the first but not the second:

print(alpha - bravo)

Output → {'Raven', 'Wolf'}

Symmetric difference — elements in either set, but not both:

print(alpha ^ bravo)

Output → {'Bull', 'Raven', 'Viper', 'Wolf'}

Checking relationships

a = {1, 2, 3}
b = {1, 2, 3, 4, 5}
print(a.issubset(b))        # True — all of a is in b
print(b.issuperset(a))      # True — b contains all of a
print(a.isdisjoint({4, 5})) # True — no elements in common

Useful patterns

Deduplicate a list and get it back as a list:

names = ["Raven", "Wolf", "Raven", "Ghost", "Wolf"]
unique = list(set(names))
print(unique)

Find common elements between two lists:

list1 = ["Raven", "Wolf", "Ghost"]
list2 = ["Ghost", "Viper", "Bull"]
common = set(list1) & set(list2)
print(common)

Output → {'Ghost'}

Heads up!

• remove() raises KeyError if missing — use discard() when unsure
• pop() on a set removes a random element — don't rely on order
• Set operations return new sets — the originals are unchanged
• You can't index a set — convert to list first if you need positional access

What you should understand now

• add() adds one element — duplicates ignored
• discard() removes safely — remove() raises an error if missing
• in checks membership — fast
• | union, & intersection, - difference, ^ symmetric difference
• Set operations return new sets — originals unchanged