📚 Dictionaries in Python for Beginners

Dictionaries in Python are one of the most powerful and versatile data structures. They allow you to store and organize data using key-value pairs, making it easy to look up and manipulate information efficiently.

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🔑 What is a Dictionary?

A dictionary is a collection of items where each item has a key and a value.
Think of it like a real phonebook — the person’s name is the key, and their phone number is the value.

Unlike lists, which are indexed by numbers, dictionaries are indexed by keys, which can be strings, numbers, or even tuples.

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📖 Example: Simple Phonebook

# Creating a dictionary
phonebook = {
    "Alice": "123-4567",
    "Bob": "987-6543"
}

# Accessing values
print(phonebook["Alice"])  # Output: 123-4567

# Adding a new entry
phonebook["Charlie"] = "555-1234"

# Updating a value
phonebook["Alice"] = "111-2222"

# Deleting an entry
del phonebook["Bob"]

print(phonebook)


# Using get() to avoid errors if key doesn't exist
print(phonebook.get("David", "Not found"))  # Output: Not found

# Using try/except
try:
    print(phonebook["David"])
except KeyError:
    print("Key not found!")


# Loop through keys and values
for name, number in phonebook.items():
    print(f"{name}: {number}")

# Loop through keys only
for name in phonebook.keys():
    print(name)

# Loop through values only
for number in phonebook.values():
    print(number)
# if statement 
if "Alice" in phonebook:
    print("Alice is in the phonebook")
    
    
# Dictionary Comprehensions 
names = ["Alice", "Bob", "Charlie"]
phonebook = {name: f"000-{i+1000}" for i, name in enumerate(names)}
print(phonebook)

# Filtering example
numbers = [100, 200, 300, 400]
squared_dict = {num: num**2 for num in numbers if num > 200}
print(squared_dict)  # Output: {300: 900, 400: 160000}


# Merging dictionaries
phonebook.update({"David": "777-8888", "Eve": "999-0000"})

# Removing items safely
removed = phonebook.pop("Alice", "Not found")
print(removed)

# Getting all keys or values
keys = list(phonebook.keys())
values = list(phonebook.values())

# Sorting a dictionary by key
sorted_phonebook = dict(sorted(phonebook.items()))
print(sorted_phonebook)

# Nested dictionaries
users = {
    "Alice": {"age": 25, "email": "alice@example.com"},
    "Bob": {"age": 30, "email": "bob@example.com"}
}
print(users["Alice"]["email"])  # Output: alice@example.com