🔑 Dictionary Basics — Key-Value Lookups

Dictionaries store data as key-value pairs, letting you look up values by meaningful names instead of numeric positions.

🎯 Creating Dictionaries

A dictionary uses curly braces `{}` and stores items as `key: value` pairs.

# Empty dictionary
empty_dict = {}

# Dictionary of student grades
grades = {"Alice": 95, "Bob": 87, "Carol": 92}

# Dictionary with mixed value types
person = {
    "name": "Alice",
    "age": 25,
    "city": "New York",
    "active": True
}

💡 Accessing Dictionary Values

Access values using the key (not an index number).

student = {"name": "Alice", "grade": "A", "score": 95}

print(student["name"])   # Alice
print(student["score"])  # 95

# Using get() - safer, returns None if key doesn't exist
print(student.get("age"))          # None
print(student.get("age", "unknown"))  # unknown (default value)

🎨 Real-World Example: Phonebook

# Store phone numbers by name
phonebook = {
    "Alice": "555-1234",
    "Bob": "555-5678",
    "Carol": "555-9012"
}

# Look up a phone number
alice_phone = phonebook["Alice"]
print(f"Alice's number: {alice_phone}")  # Alice's number: 555-1234

# Check if a key exists
if "David" in phonebook:
    print(phonebook["David"])
else:
    print("David not in phonebook")

📊 Dictionary vs List

🔑 Key Takeaways

• ✅ Dictionaries use `key: value` pairs

• ✅ Access values with `dict[key]` notation

• ✅ Keys must be unique (usually strings or numbers)

• ✅ Use `.get()` to safely access keys

• ✅ Check if key exists with `in` operator

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