Sets

def main():
    # Create a set of tags for a blog post
    tags = set()
    
    print("=== Adding Blog Tags ===")
    
    # Add tags
    tags.add("python")
    print(f"Added 'python': {tags}")
    
    tags.add("programming")
    print(f"Added 'programming': {tags}")
    
    tags.add("tutorial")
    print(f"Added 'tutorial': {tags}")
    
    # Try to add duplicate
    tags.add("python")
    print(f"Added 'python' again: {tags}")
    print("Duplicate ignored!")
    
    # Add more tags
    tags.add("beginner")
    tags.add("coding")
    tags.add("python")
    print(f"\nWith more tags: {tags}")
    
    print("\n=== Blog Post Tags ===")
    print(f"Total unique tags: {len(tags)}")
    print(f"Tags: {tags}")
    
    # Display as hashtags
    print("\n=== Formatted ===")
    hashtags = " ".join(f"#{tag}" for tag in tags)
    print(hashtags)
    
    # Alternative creation with literal
    print("\n=== Set Literal ===")
    colors = {"red", "green", "blue"}  # Note: {} is empty dict, not set!
    print(f"Colors: {colors}")

main()

def main():
    # Create an allowlist of premium users
    premium_users = {"alice", "bob", "carol", "david"}
    
    print("=== Premium Membership ===")
    print(f"Premium users: {premium_users}")
    
    # Check if user has access
    current_user = "eve""bob"
    
    print("\n=== Access Check ===")
    print(f"User: {current_user}")
    
    if current_user in premium_users:
        print("✓ Premium access granted!")
        print("Welcome to exclusive content.")
    else:
        print("✗ Not a premium user.")
        print("Upgrade to access premium features!")
    
    # Blocked users check
    blocked_users = {"spammer", "troll", "eve"}
    
    print("\n=== Security Check ===")
    if current_user in blocked_users:
        print("⛔ User is blocked!")
    else:
        print("✓ User is not blocked.")
    
    # Check multiple users
    print("\n=== Batch Check ===")
    users_to_check = ["alice", "eve", "bob", "frank"]
    
    for user in users_to_check:
        status = "Premium" if user in premium_users else "Regular"
        print(f"{user}: {status}")
    
    # Speed comparison note
    print("\n=== Performance Note ===")
    print("'in' check for set: O(1) - instant!")
    print("'in' check for list: O(n) - slower")

main()

def main():
    # Create an allowlist of premium users
    premium_users = {"alice", "bob", "carol", "david"}
    
    print("=== Premium Membership ===")
    print(f"Premium users: {premium_users}")
    
    # Check if user has access
    current_user = "eve""bob"
    
    print("\n=== Access Check ===")
    print(f"User: {current_user}")
    
    if current_user in premium_users:
        print("✓ Premium access granted!")
        print("Welcome to exclusive content.")
    else:
        print("✗ Not a premium user.")
        print("Upgrade to access premium features!")
    
    # Blocked users check
    blocked_users = {"spammer", "troll", "eve"}
    
    print("\n=== Security Check ===")
    if current_user in blocked_users:
        print("⛔ User is blocked!")
    else:
        print("✓ User is not blocked.")
    
    # Check multiple users
    print("\n=== Batch Check ===")
    users_to_check = ["alice", "eve", "bob", "frank"]
    
    for user in users_to_check:
        status = "Premium" if user in premium_users else "Regular"
        print(f"{user}: {status}")
    
    # Speed comparison note
    print("\n=== Performance Note ===")
    print("'in' check for set: O(1) - instant!")
    print("'in' check for list: O(n) - slower")

main()

def main():
    cart = {"Laptop", "Mouse", "Keyboard", "Monitor", "Headphones"}
    
    print("=== Shopping Cart ===")
    print(f"Items: {cart}")
    print(f"Count: {len(cart)}")
    
    # remove() vs discard()
    print("\n=== Removing Items ===")
    
    # remove() raises KeyError if not found
    to_remove = "Mouse"
    cart.remove(to_remove)
    print(f"Removed '{to_remove}': {cart}")
    
    # discard() does nothing if not found (no error!)
    not_in_cart = "Tablet"
    cart.discard(not_in_cart)
    print(f"Discard '{not_in_cart}' (not in cart): no error!")
    print(f"Cart unchanged: {cart}")
    
    # This would cause error:
    # cart.remove("Tablet")  # KeyError!
    
    # Remove more items
    cart.discard("Keyboard")
    cart.discard("Monitor")
    print(f"\nAfter more removals: {cart}")
    
    # Clear all
    print("\n=== Clearing Cart ===")
    print(f"Before clear: {len(cart)} items")
    cart.clear()
    print(f"After clear: {len(cart)} items")
    print(f"Cart is empty: {len(cart) == 0}")
    
    # pop() - remove arbitrary item
    demo_set = {1, 2, 3, 4, 5}
    print("\n=== pop() Demo ===")
    print(f"Set: {demo_set}")
    popped = demo_set.pop()  # Removes and returns ONE item
    print(f"Popped: {popped}")
    print(f"Remaining: {demo_set}")

main()

def main():
    # Two teams' skill sets
    team_a = {"Java", "Python", "SQL", "Git"}
    team_b = {"JavaScript", "Python", "CSS", "Git"}
    
    print("=== Team Skills ===")
    print(f"Team A: {team_a}")
    print(f"Team B: {team_b}")
    
    # Union: All skills combined
    all_skills = team_a | team_b  # Or: team_a.union(team_b)
    
    print("\n=== Union (All Skills) ===")
    print(f"Combined: {all_skills}")
    print("(Duplicates automatically removed)")
    
    # Alternative syntax
    all_skills_method = team_a.union(team_b)
    print(f"Using .union(): {all_skills_method}")
    
    # Count unique skills
    print("\n=== Statistics ===")
    print(f"Team A skills: {len(team_a)}")
    print(f"Team B skills: {len(team_b)}")
    print(f"Unique combined: {len(all_skills)}")
    overlap = len(team_a) + len(team_b) - len(all_skills)
    print(f"Overlap count: {overlap}")
    
    # Practical example: Merge user permissions
    print("\n=== Permission Merge ===")
    
    basic_perms = {"read", "comment"}
    editor_perms = {"read", "write", "edit", "comment"}
    admin_perms = {"read", "write", "edit", "delete", "manage"}
    
    # Build editor permissions (basic + editor)
    full_editor_perms = basic_perms | editor_perms
    print(f"Editor has: {full_editor_perms}")
    
    # Build admin permissions (all combined)
    full_admin_perms = basic_perms | editor_perms | admin_perms
    print(f"Admin has: {full_admin_perms}")
    
    # Update in place with |=
    user_perms = {"read"}
    user_perms |= {"comment", "vote"}  # Add more
    print(f"\nUser perms after |=: {user_perms}")

main()

def main():
    # List with duplicate entries
    emails = [
        "alice@example.com",
        "bob@example.com",
        "alice@example.com",  # duplicate
        "carol@example.com",
        "bob@example.com",    # duplicate
        "david@example.com",
        "alice@example.com"   # duplicate
    ]
    
    print("=== Email List (with duplicates) ===")
    print(f"Emails: {emails}")
    print(f"Count: {len(emails)}")
    
    # Remove duplicates using set
    unique_emails = set(emails)
    
    print("\n=== After Removing Duplicates ===")
    print(f"Unique: {unique_emails}")
    print(f"Count: {len(unique_emails)}")
    print(f"Removed {len(emails) - len(unique_emails)} duplicates")
    
    # Convert back to list if needed
    cleaned_list = list(unique_emails)
    print(f"\nAs list: {cleaned_list}")
    
    # PRESERVE ORDER: use dict.fromkeys()
    print("\n=== Preserving Order ===")
    ordered_unique = list(dict.fromkeys(emails))
    print(f"Order preserved: {ordered_unique}")
    print("(dict maintains insertion order in Python 3.7+)")
    
    # One-liner pattern
    print("\n=== One-liner Dedup ===")
    nums = [3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5]
    unique_nums = list(set(nums))
    print(f"Original: {nums}")
    print(f"Unique (order lost): {unique_nums}")
    
    # Duplicate analysis
    print("\n=== Duplicate Analysis ===")
    from collections import Counter
    counts = Counter(emails)
    
    for email, count in counts.items():
        if count > 1:
            print(f"{email} appeared {count} times")

main()