Quest 7: Dictionaries - The Key Keeper

Store Data in Key-Value Pairs

🗝️ QUEST 7 | Difficulty: Intermediate | Time: 5 minutes

📊 Complexity Level: Intermediate ⭐⭐

Builds on fundamental concepts from earlier quests. Best for students who have completed Quests 1-6 or have some basic programming experience. This introduces more advanced data structures.

📖 Introduction: The Magic Phonebook

You’re keeping track of your friends’ phone numbers. With a list, you’d have:

names = ["Alice", "Bob", "Charlie"]
phones = ["555-1234", "555-5678", "555-9012"]
# Which number belongs to who? Confusing!

What if you could look up numbers by name, like a phonebook? That’s what dictionaries do! They store data in key-value pairs.

🗃️ Story Time: You’ve discovered a magical filing cabinet. Instead of folders numbered 0, 1, 2 (like lists), each folder has a label: “Health Potions”, “Gold Coins”, “Magic Spells”. You can instantly find what you need by its name, not by remembering its position!

💡 Explanation: What are Dictionaries?

A dictionary stores data as key-value pairs: - Key: The label (like “name” or “health”) - Value: The data (like “Hero” or 100)

# Creating dictionaries
player = {
    "name": "Hero",
    "level": 5,
    "health": 100,
    "inventory": ["sword", "shield"]
}

# Access values by key
print(player["name"])  # "Hero"
print(player["level"]) # 5

🎯 Dictionary vs List:

List: Ordered, accessed by numeric index

items = ["sword", "shield", "potion"]
print(items[0])  # "sword"

Dictionary: Key-value pairs, accessed by key

stats = {"strength": 10, "speed": 15}
print(stats["strength"])  # 10

When to use what? - List: When order matters, or you have simple collections - Dictionary: When you need to look up values by name/label

🎮 Activity: Character Stats

Create and manage a character using a dictionary:

🎯 Challenge:

Create a dictionary for a wizard character with different stats
Give the wizard high intelligence (30) but low strength (5)
Add a “spells” key with a list of spell names
Print the wizard’s info in a nice format

👨‍💻 Code Example: Inventory System

Dictionaries are perfect for managing game inventories:

💡 Dictionary Methods:

dict.keys() - Get all keys
dict.values() - Get all values
dict.items() - Get all key-value pairs
dict.get(key, default) - Safely get value (returns default if key doesn’t exist)
dict.pop(key) - Remove and return value
dict.update(other_dict) - Merge dictionaries

stats = {"hp": 100, "mp": 50}
print(stats.keys())    # dict_keys(['hp', 'mp'])
print(stats.values())  # dict_values([100, 50])
print(stats.get("hp", 0))  # 100
print(stats.get("xp", 0))  # 0 (default since "xp" doesn't exist)

🧩 Puzzle Time!

What will this code create? Predict the output:

🔑 Solution Explained:

The output is:

Scores Dictionary:
  level_1: 150
  level_2: 150
  total: 300

Step-by-step trace:

Start with empty dictionary: {}
Add level_1: {"level_1": 100}
Add level_2: {"level_1": 100, "level_2": 150}
Update level_1 to 100 + 50 = 150: {"level_1": 150, "level_2": 150}
Add total = 150 + 150 = 300: {"level_1": 150, "level_2": 150, "total": 300}

Key insight: When you assign to an existing key (like scores["level_1"]), it updates the value instead of creating a duplicate key. Dictionary keys are unique!

🎮 Bonus: Nested Dictionaries

Dictionaries can contain other dictionaries for complex data:

🎯 Key Takeaways

✨ Quest 7 Complete! ✨

You’ve learned:

✅ Dictionaries store key-value pairs
✅ Access values using keys: dict[key]
✅ Keys must be unique; values can be any type
✅ Use .items(), .keys(), .values() to iterate
✅ Dictionaries can be nested for complex data
✅ Use .get() for safe access with defaults

Next Quest: Ready for beautiful patterns? Try Quest 8: Fibonacci!

🚀 Try This at Home!

Create a contacts app:

contacts = {
    "Alice": {"phone": "555-1234", "email": "[email protected]"},
    "Bob": {"phone": "555-5678", "email": "[email protected]"},
    "Charlie": {"phone": "555-9012", "email": "[email protected]"}
}

# Look up a contact
name = "Alice"
if name in contacts:
    print(f"{name}'s phone: {contacts[name]['phone']}")

Or a simple game state manager:

game_state = {
    "current_level": 1,
    "player": {
        "health": 100,
        "position": {"x": 0, "y": 0}
    },
    "enemies": {
        "goblin_1": {"health": 30, "position": {"x": 10, "y": 5}},
        "goblin_2": {"health": 30, "position": {"x": 15, "y": 8}}
    }
}

print(f"Level: {game_state['current_level']}")
print(f"Player health: {game_state['player']['health']}")

📱 Outstanding! Dictionaries are everywhere in real programs. You’re becoming a pro! 💼

--- title: "Quest 7: Dictionaries - The Key Keeper" subtitle: "Store Data in Key-Value Pairs" format: live-html: code-tools: true --- ::: {.quest-badge} 🗝️ QUEST 7 | Difficulty: Intermediate | Time: 5 minutes ::: ::: {.concept-box} **📊 Complexity Level: Intermediate ⭐⭐** Builds on fundamental concepts from earlier quests. Best for students who have completed Quests 1-6 or have some basic programming experience. This introduces more advanced data structures. ::: ## 📖 Introduction: The Magic Phonebook You're keeping track of your friends' phone numbers. With a list, you'd have: ```python names = ["Alice", "Bob", "Charlie"] phones = ["555-1234", "555-5678", "555-9012"] # Which number belongs to who? Confusing! ``` What if you could look up numbers by name, like a phonebook? That's what **dictionaries** do! They store data in **key-value pairs**. ::: {.story-box} **🗃️ Story Time**: You've discovered a magical filing cabinet. Instead of folders numbered 0, 1, 2 (like lists), each folder has a label: "Health Potions", "Gold Coins", "Magic Spells". You can instantly find what you need by its name, not by remembering its position! ::: ## 💡 Explanation: What are Dictionaries? A **dictionary** stores data as key-value pairs: - **Key**: The label (like "name" or "health") - **Value**: The data (like "Hero" or 100) ```python # Creating dictionaries player = { "name": "Hero", "level": 5, "health": 100, "inventory": ["sword", "shield"] } # Access values by key print(player["name"]) # "Hero" print(player["level"]) # 5 ``` ::: {.concept-box} **🎯 Dictionary vs List**: **List**: Ordered, accessed by numeric index ```python items = ["sword", "shield", "potion"] print(items[0]) # "sword" ``` **Dictionary**: Key-value pairs, accessed by key ```python stats = {"strength": 10, "speed": 15} print(stats["strength"]) # 10 ``` **When to use what?** - **List**: When order matters, or you have simple collections - **Dictionary**: When you need to look up values by name/label ::: ## 🎮 Activity: Character Stats Create and manage a character using a dictionary: ```{pyodide-python} # Create a character dictionary character = { "name": "Dragon Slayer", "class": "Warrior", "level": 10, "health": 150, "mana": 50, "strength": 25, "intelligence": 12 } print("=== CHARACTER SHEET ===") for key, value in character.items(): print(f"{key.title()}: {value}") print("=" * 30) print() # Update values character["health"] = 200 print(f"Health increased to {character['health']}!") print() # Add new key-value pairs character["gold"] = 1000 character["location"] = "Dark Forest" print("Added gold and location!") print(f"Gold: {character['gold']}") print(f"Current location: {character['location']}") print() # Check if a key exists if "magic_resistance" in character: print("Has magic resistance") else: print("No magic resistance - adding it now!") character["magic_resistance"] = 10 # Try adding your own stats! ``` ::: {.challenge-box} **🎯 Challenge**: 1. Create a dictionary for a wizard character with different stats 2. Give the wizard high intelligence (30) but low strength (5) 3. Add a "spells" key with a list of spell names 4. Print the wizard's info in a nice format ::: ## 👨‍💻 Code Example: Inventory System Dictionaries are perfect for managing game inventories: ```{pyodide-python} # Item database using nested dictionaries items = { "health_potion": { "name": "Health Potion", "effect": "heal", "power": 50, "price": 25 }, "mana_potion": { "name": "Mana Potion", "effect": "restore_mana", "power": 30, "price": 20 }, "sword": { "name": "Iron Sword", "effect": "attack", "power": 35, "price": 100 } } # Player inventory (item_id: quantity) player_inventory = { "health_potion": 3, "mana_potion": 2, "sword": 1 } print("=== INVENTORY ===") for item_id, quantity in player_inventory.items(): item_info = items[item_id] print(f"{item_info['name']} x{quantity}") print(f" Effect: {item_info['effect']} (+{item_info['power']})") print() # Calculate total inventory value total_value = 0 for item_id, quantity in player_inventory.items(): total_value += items[item_id]["price"] * quantity print(f"Total inventory value: {total_value} gold") ``` ::: {.tip-box} **💡 Dictionary Methods**: - `dict.keys()` - Get all keys - `dict.values()` - Get all values - `dict.items()` - Get all key-value pairs - `dict.get(key, default)` - Safely get value (returns default if key doesn't exist) - `dict.pop(key)` - Remove and return value - `dict.update(other_dict)` - Merge dictionaries ```python stats = {"hp": 100, "mp": 50} print(stats.keys()) # dict_keys(['hp', 'mp']) print(stats.values()) # dict_values([100, 50]) print(stats.get("hp", 0)) # 100 print(stats.get("xp", 0)) # 0 (default since "xp" doesn't exist) ``` ::: ## 🧩 Puzzle Time! What will this code create? Predict the output: ```{pyodide-python} # The Score Tracker scores = {} # Add scores scores["level_1"] = 100 scores["level_2"] = 150 scores["level_1"] = scores["level_1"] + 50 # Update level_1 # Add total scores["total"] = scores["level_1"] + scores["level_2"] print("Scores Dictionary:") for level, score in scores.items(): print(f" {level}: {score}") # What's in the dictionary? # What's the total? ``` ::: {.solution-box} **🔑 Solution Explained**: The output is: ``` Scores Dictionary: level_1: 150 level_2: 150 total: 300 ``` **Step-by-step trace**: 1. Start with empty dictionary: `{}` 2. Add `level_1`: `{"level_1": 100}` 3. Add `level_2`: `{"level_1": 100, "level_2": 150}` 4. **Update** `level_1` to 100 + 50 = 150: `{"level_1": 150, "level_2": 150}` 5. Add `total` = 150 + 150 = 300: `{"level_1": 150, "level_2": 150, "total": 300}` **Key insight**: When you assign to an existing key (like `scores["level_1"]`), it **updates** the value instead of creating a duplicate key. Dictionary keys are unique! ::: ## 🎮 Bonus: Nested Dictionaries Dictionaries can contain other dictionaries for complex data: ```{pyodide-python} # RPG party system party = { "warrior": { "name": "Thorin", "level": 12, "stats": {"strength": 25, "intelligence": 10}, "equipment": ["sword", "shield", "armor"] }, "mage": { "name": "Gandalf", "level": 15, "stats": {"strength": 8, "intelligence": 30}, "equipment": ["staff", "robe", "hat"] }, "rogue": { "name": "Shadow", "level": 10, "stats": {"strength": 15, "intelligence": 18}, "equipment": ["dagger", "cloak", "lockpicks"] } } print("=== PARTY ROSTER ===") for role, character in party.items(): print(f"\n{role.upper()}: {character['name']} (Level {character['level']})") print(f" Strength: {character['stats']['strength']}") print(f" Intelligence: {character['stats']['intelligence']}") print(f" Equipment: {', '.join(character['equipment'])}") # Access nested data print(f"\n🧙 The mage's intelligence is: {party['mage']['stats']['intelligence']}") ``` ## 🎯 Key Takeaways ::: {.quest-complete} ### ✨ Quest 7 Complete! ✨ You've learned: ✅ Dictionaries store key-value pairs ✅ Access values using keys: `dict[key]` ✅ Keys must be unique; values can be any type ✅ Use `.items()`, `.keys()`, `.values()` to iterate ✅ Dictionaries can be nested for complex data ✅ Use `.get()` for safe access with defaults **Next Quest**: Ready for beautiful patterns? Try [Quest 8: Fibonacci](08-fibonacci.qmd)! ::: ## 🚀 Try This at Home! Create a contacts app: ```python contacts = { "Alice": {"phone": "555-1234", "email": "[email protected]"}, "Bob": {"phone": "555-5678", "email": "[email protected]"}, "Charlie": {"phone": "555-9012", "email": "[email protected]"} } # Look up a contact name = "Alice" if name in contacts: print(f"{name}'s phone: {contacts[name]['phone']}") ``` Or a simple game state manager: ```python game_state = { "current_level": 1, "player": { "health": 100, "position": {"x": 0, "y": 0} }, "enemies": { "goblin_1": {"health": 30, "position": {"x": 10, "y": 5}}, "goblin_2": {"health": 30, "position": {"x": 15, "y": 8}} } } print(f"Level: {game_state['current_level']}") print(f"Player health: {game_state['player']['health']}") ``` --- ::: {.tip-box} **📱 Outstanding!** Dictionaries are everywhere in real programs. You're becoming a pro! 💼 :::