Dictionaries in Python: Storing Data as Key-Value Pairs 📖

Imagine you’re creating a character card for a game. The character has a name, attack, health, and class. How do you keep all of that together?

You could create multiple variables:

hero_name = "Arthur"
hero_attack = 15
hero_health = 100
hero_class = "Warrior"

But that’s inconvenient! What if there are many characters? You need something better.

🗂️ What Is a Dictionary?

A dictionary is like a box with labeled tabs. Each tab has a name (key), and the value sits behind it.

In a regular dictionary:
- Word (key) → Definition (value)
- “Dragon” → “A mythical creature that breathes fire”

In a Python dictionary:
- Key → Value
- "name" → "Arthur"
- "attack" → 15

🎮 Creating Your First Dictionary

A dictionary is created with curly braces { }:

hero = {
    "name": "Arthur",
    "attack": 15,
    "health": 100
}

Syntax:
- Curly braces { }
- key: value pairs
- Separated by commas
- Keys are usually strings (in quotes)

📥 Reading Values from a Dictionary

Use square brackets with the key to retrieve a value:

hero = {
    "name": "Arthur",
    "attack": 15,
    "health": 100
}

print(hero["name"])     # Arthur
print(hero["attack"])   # 15
print(hero["health"])   # 100

Important: Use exactly the same key you defined!

✏️ Changing Values

You can update any value in the dictionary:

hero = {"name": "Arthur", "health": 100}

print(f"Health: {hero['health']}")  # 100

# Hero takes damage
hero["health"] = 80

print(f"Health after hit: {hero['health']}")  # 80

# You can use arithmetic
hero["health"] = hero["health"] - 20  # Subtract 20
print(f"Health: {hero['health']}")  # 60

# Shorthand
hero["health"] -= 15  # Another -15
print(f"Health: {hero['health']}")  # 45

➕ Adding New Keys

Just assign a value to a new key:

hero = {
    "name": "Arthur",
    "health": 100
}

# Add new fields
hero["level"] = 1
hero["exp"] = 0

print(hero)
# {'name': 'Arthur', 'health': 100, 'level': 1, 'exp': 0}

🐲 Practical Example: Monster Card

dragon = {
    "name": "🐲 Fire Dragon",
    "attack": 25,
    "health": 150,
    "type": "fire"
}

print(f"Opponent: {dragon['name']}")
print(f"Attack: {dragon['attack']}")
print(f"Health: {dragon['health']}")
print(f"Type: {dragon['type']}")

# Dragon attacks the hero
hero_health = 100
damage = dragon["attack"]
hero_health -= damage

print(f"\n💥 Dragon attacked! Damage: {damage}")
print(f"Hero health: {hero_health}")

Output:

Opponent: 🐲 Fire Dragon
Attack: 25
Health: 150
Type: fire

💥 Dragon attacked! Damage: 25
Hero health: 75

📋 List of Dictionaries: A Collection of Objects

The most powerful pattern — you can create a list of dictionaries! Think of it as a deck of cards where each card is a separate dictionary:

creatures = [
    {"name": "🐲 Dragon", "attack": 8, "health": 12},
    {"name": "🧙 Mage", "attack": 6, "health": 8},
    {"name": "⚔️ Knight", "attack": 5, "health": 10}
]

# Print all creatures
for creature in creatures:
    print(f"{creature['name']} - ATK: {creature['attack']}, HP: {creature['health']}")

Output:

🐲 Dragon - ATK: 8, HP: 12
🧙 Mage - ATK: 6, HP: 8
⚔️ Knight - ATK: 5, HP: 10

🎯 Value Types in a Dictionary

A dictionary can hold any data types:

player = {
    "name": "Player1",           # string
    "level": 5,                  # integer
    "health": 100.5,             # float
    "is_alive": True,            # boolean
    "inventory": ["sword", "shield"]  # list
}

print(f"Name: {player['name']}")
print(f"Level: {player['level']}")
print(f"Alive: {player['is_alive']}")
print(f"Inventory: {player['inventory']}")

⚠️ Common Mistakes

1. Wrong Key

hero = {"name": "Arthur", "health": 100}

# ❌ ERROR: KeyError
print(hero["Name"])  # Capital N — that's a different key!

# ✅ CORRECT
print(hero["name"])  # Exactly as defined

2. Forgot Quotes Around the Key

# ❌ ERROR
hero = {name: "Arthur"}  # name without quotes

# ✅ CORRECT
hero = {"name": "Arthur"}

3. Missing Commas Between Pairs

# ❌ ERROR: missing comma
hero = {
    "name": "Arthur"
    "health": 100
}

# ✅ CORRECT
hero = {
    "name": "Arthur",
    "health": 100
}

📊 Comparison: List vs Dictionary

When to use a list:
- A collection of similar things
- planets = ["Mars", "Venus", "Jupiter"]
- Order is important

When to use a dictionary:
- Describing a single object
- hero = {"name": "Arthur", "level": 5}
- Named fields are needed

🎯 Summary

Remember:
- ✅ A dictionary is made of key: value pairs
- ✅ Use curly braces { }
- ✅ Access values via dictionary["key"]
- ✅ You can modify and add fields
- ✅ Perfect for storing object attributes