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")

set_a = {1, 2, 3}
set_b = {3, 4, 5}

# Using method
print(set_a.union(set_b))          # {1, 2, 3, 4, 5}
# Using operator
print(set_a | set_b)               # {1, 2, 3, 4, 5}

# Using method
print(set_a.intersection(set_b))   # {3}
# Using operator
print(set_a & set_b)               # {3}

# Using method (A - B)
print(set_a.difference(set_b))     # {1, 2}
# Using operator
print(set_a - set_b)               # {1, 2}

# Using method
print(set_a.symmetric_difference(set_b)) # {1, 2, 4, 5}
# Using operator
print(set_a ^ set_b)                     # {1, 2, 4, 5}

small_set = {1, 2}
big_set = {1, 2, 3, 4}

# Check if small_set is a subset of big_set (<=)
print(small_set.issubset(big_set))     # True
print(small_set <= big_set)            # True

# Check if big_set is a superset of small_set (>=)
print(big_set.issuperset(small_set))   # True
print(big_set >= small_set)            # True

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")