Dictionaries in Python

# Different ways to create dictionaries

# Empty dictionary
my_dict = {}
print("Empty:", my_dict)

# Dictionary with data
person = {
    "name": "Alice",
    "age": 25,
    "city": "London"
}
print("Person:", person)

# Using dict() constructor
info = dict(name="Bob", age=30, job="Developer")
print("Info:", info)

# Mixed value types
product = {
    "id": 101,
    "name": "Laptop",
    "price": 999.99,
    "in_stock": True
}
print("Product:", product)

person = {"name": "Alice", "age": 25}

# Method 1: Square brackets (fast but risky)
print("Name:", person["name"])

# Method 2: .get() method (safe)
print("Age:", person.get("age"))

# .get() with missing key
print("Email:", person.get("email"))          # Returns None
print("Email:", person.get("email", "N/A"))   # Returns "N/A"

# Square brackets with missing key would crash:
# print(person["email"])  # KeyError!

person = {"name": "Alice"}
print("Start:", person)

# Add new key-value pair
person["age"] = 25
print("After adding age:", person)

# Add another
person["city"] = "London"
print("After adding city:", person)

# Change existing value
person["age"] = 26
print("After changing age:", person)

# Add multiple with .update()
person.update({"job": "Developer", "country": "UK"})
print("After update:", person)

person = {"name": "Alice", "age": 25, "city": "London"}
print("Start:", person)

# del - delete by key
del person["city"]
print("After del:", person)

# pop - remove and get the value
age = person.pop("age")
print(f"Popped age: {age}")
print("After pop:", person)

# pop with default (safe)
job = person.pop("job", "Not found")
print(f"Popped job: {job}")

person = {"name": "Alice", "age": 25}

# Check if key exists
if "name" in person:
    print("Name found:", person["name"])

if "email" in person:
    print("Email:", person["email"])
else:
    print("Email not found")

# Check if key does NOT exist
if "phone" not in person:
    print("Phone number not stored")

# Practical pattern: safe access
key = "city"
if key in person:
    print(f"{key}: {person[key]}")
else:
    print(f"{key} is not in the dictionary")

person = {"name": "Alice", "age": 25, "city": "London"}

# Loop through keys (default)
print("Keys:")
for key in person:
    print(f"  {key}")

# Loop through values
print("\nValues:")
for value in person.values():
    print(f"  {value}")

# Loop through key-value pairs (most common)
print("\nKey-Value pairs:")
for key, value in person.items():
    print(f"  {key}: {value}")

person = {"name": "Alice", "age": 25, "city": "London"}

# Get all keys
print("Keys:", list(person.keys()))

# Get all values
print("Values:", list(person.values()))

# Get all items as tuples
print("Items:", list(person.items()))

# Count pairs
print(f"Number of items: {len(person)}")

# Make a copy
person_copy = person.copy()
person_copy["name"] = "Bob"
print(f"Original name: {person['name']}")
print(f"Copy name: {person_copy['name']}")

# Nested dictionary - users with details
users = {
    "user1": {
        "name": "Alice",
        "age": 25,
        "email": "alice@email.com"
    },
    "user2": {
        "name": "Bob",
        "age": 30,
        "email": "bob@email.com"
    }
}

# Access nested values
print("User1 name:", users["user1"]["name"])
print("User2 email:", users["user2"]["email"])

# Loop through nested dict
print("\nAll users:")
for user_id, info in users.items():
    print(f"  {user_id}: {info['name']} ({info['
...

# Create a dictionary of squares
squares = {x: x**2 for x in range(1, 6)}
print("Squares:", squares)

# Create from two lists
names = ["Alice", "Bob", "Charlie"]
ages = [25, 30, 35]
people = {name: age for name, age in zip(names, ages)}
print("People:", people)

# With condition
even_squares = {x: x**2 for x in range(10) if x % 2 == 0}
print("Even squares:", even_squares)