Sets

# Empty set (careful!)
empty_set = set()  # NOT {} - that's a dict!

# Set with values - both ways work
numbers = {1, 2, 3, 4, 5}
fruits = set(["apple", "banana", "orange"])

# From a list (removes duplicates)
scores = [85, 90, 85, 92, 90]
unique_scores = set(scores)  # {85, 90, 92}

colors = {"red", "blue"}

# Add items
colors.add("green")
print(colors)  # {'red', 'blue', 'green'}

# Remove items
colors.remove("blue")    # Error if not found
colors.discard("yellow") # No error if not found

# Check membership
if "red" in colors:
    print("Red is available")

names = ["Alice", "Bob", "Alice", "Charlie", "Bob"]
unique_names = list(set(names))
print(unique_names)  # ['Alice', 'Bob', 'Charlie']

allowed_users = {"alice", "bob", "charlie"}

if "alice" in allowed_users:  # Very fast!
    print("Access granted")