# Variables are created on assignment
name = "Alice"
age = 25
height = 5.7
is_active = True

print(name)      # Alice
print(age)       # 25
print(height)    # 5.7
print(is_active) # True

x = 10
message = "Hello"
pi = 3.14159

# Assign the same value to multiple variables
a = b = c = 100
print(a, b, c)  # 100 100 100

# Assign different values in one line
x, y, z = 1, 2, 3
print(x, y, z)  # 1 2 3

# Swap variables (no temp variable needed!)
a, b = 10, 20
a, b = b, a
print(a, b)  # 20 10

# Unpack a list
colors = ["red", "green", "blue"]
r, g, b = colors
print(r)  # red

# Unpack with * (catch remaining items)
first, *rest = [1, 2, 3, 4, 5]
print(first)  # 1
print(rest)   # [2, 3, 4, 5]

first, *middle, last = [1, 2, 3, 4, 5]
print(middle)  # [2, 3, 4]

x = 10          # int
x = "hello"     # now it's a str
x = [1, 2, 3]   # now it's a list

print(type(x))  # <class 'list'>

# String to integer
age = int("25")
print(age + 5)  # 30

# Integer to string
num = str(100)
print("Score: " + num)  # Score: 100

# String to float
price = float("19.99")
print(price)  # 19.99

# Float to integer (truncates)
x = int(3.99)
print(x)  # 3

# To boolean
print(bool(0))      # False
print(bool(1))      # True
print(bool(""))     # False
print(bool("text")) # True
print(bool([]))     # False
print(bool([1]))    # True

def greet():
    message = "Hello!"  # Local variable
    print(message)

greet()        # Hello!
# print(message)  # NameError: name 'message' is not defined

name = "Alice"  # Global variable

def greet():
    print(f"Hello, {name}")  # Can read global variables

greet()  # Hello, Alice

counter = 0

def increment():
    global counter
    counter += 1

increment()
increment()
print(counter)  # 2

def outer():
    count = 0

    def inner():
        nonlocal count
        count += 1

    inner()
    inner()
    print(count)  # 2

outer()

# Constants (by convention)
MAX_SIZE = 100
PI = 3.14159
DATABASE_URL = "postgresql://localhost/mydb"
API_KEY = "abc123"

# These CAN be changed (Python won't prevent it)
# but developers know they SHOULDN'T be changed

x = 10
print(x)  # 10

del x
# print(x)  # NameError: name 'x' is not defined

a = 10
b = 10
print(id(a))  # e.g., 140234567890
print(id(b))  # Same as above! (Python caches small integers)
print(a is b)  # True (same object)

c = [1, 2, 3]
d = [1, 2, 3]
print(c == d)   # True (same value)
print(c is d)   # False (different objects)
print(id(c) == id(d))  # False

"""
Demonstrates Python variable concepts.
"""

# Constants
TAX_RATE = 0.08
STORE_NAME = "Python Shop"

def calculate_total(price, quantity):
    """Calculate total with tax."""
    subtotal = price * quantity
    tax = subtotal * TAX_RATE
    total = subtotal + tax
    return total, subtotal, tax

# Multiple assignment
item_name, item_price, item_qty = "Widget", 29.99, 3

# Unpacking return values
total, subtotal, tax = calculate_total(item_price, item_qty)

# Formatted output
print(f"{'=' * 30}")
print(f"  {STORE_NAME}")
print(f"{'=' * 30}")
print(f"  Item:     {item_name}")
print(f"  Price:    ${item_price:.2f}")
print(f"  Quantity: {item_qty}")
print(f"  Subtotal: ${subtotal:.2f}")
print(f"  Tax:      ${tax:.2f}")
print(f"  Total:    ${total:.2f}")
print(f"{'=' * 30}")

==============================
  Python Shop
==============================
  Item:     Widget
  Price:    $29.99
  Quantity: 3
  Subtotal: $89.97
  Tax:      $7.20
  Total:    $97.17
==============================