Manage Unique Items and Perform Fast Membership Checks with Sets

# Create a set from a list (duplicates are automatically removed)
user_ids_list = [101, 203, 101, 405, 203, 506]
unique_user_ids = set(user_ids_list)
print(f"Unique User IDs: {unique_user_ids}")

# Add elements to a set
unique_user_ids.add(607)
print(f"After adding 607: {unique_user_ids}")
unique_user_ids.add(101) # Adding an existing element has no effect
print(f"After adding existing 101: {unique_user_ids}")

# Remove elements from a set
unique_user_ids.discard(405) # discard() doesn't raise error if item not found
print(f"After discarding 405: {unique_user_ids}")
# unique_user_ids.remove(999) # remove() raises KeyError if item not found

# Efficient membership testing (O(1) on average)
print(f"Is 203 in set? {203 in unique_user_ids}")
print(f"Is 999 in set? {999 in unique_user_ids}")

# Set operations: union, intersection, difference
admin_users = {101, 304, 506}
premium_users = {203, 506, 607}

all_special_users = admin_users.union(premium_users) # or admin_users | premium_users
print(f"All special users (union): {all_special_users}")

admin_and_premium = admin_users.intersection(premium_users) # or admin_users & premium_users
print(f"Admin AND Premium users (intersection): {admin_and_premium}")

only_admin = admin_users.difference(premium_users) # or admin_users - premium_users
print(f"Only Admin users (difference): {only_admin}")

# Example: Check for new items in a list against existing items
existing_tags = {'python', 'webdev', 'flask'}
new_tags_input = ['python', 'django', 'api', 'flask']
newly_added_tags = set(new_tags_input) - existing_tags
print(f"New tags to add: {newly_added_tags}")