# and: if the first operand is False, the second is not evaluated
False and print("This never runs")  # False

# or: if the first operand is True, the second is not evaluated
True or print("This never runs")  # True

# and returns the first falsy value, or the last value
print(0 and 5)  # 0 (0 is falsy → stops here)
print("" and "hello")  # "" (empty string is falsy)
print(None and 42)  # None (None is falsy)

print(1 and 5)  # 5 (1 is truthy → goes to next → returns 5)
print("hello" and 42)  # 42 (both truthy → returns the last value)
print(3 and 2 and 1)  # 1 (all truthy → returns the last value)
print(3 and 0 and 1)  # 0 (stops at 0)

# These all evaluate to False
bool(False)  # False
bool(0)  # False
bool(0.0)  # False
bool("")  # False
bool(None)  # False
bool([])  # False (empty list)
bool({})  # False (empty dictionary)

# Everything else is True
bool(1)  # True
bool("hello")  # True
bool([1, 2])  # True

# or returns the first truthy value, or the last value
print(0 or 5)  # 5 (0 is falsy → goes to next → returns 5)
print("" or "hello")  # "hello" (empty string is falsy → returns "hello")
print(None or 42)  # 42

print(1 or 5)  # 1 (1 is truthy → stops here)
print("hi" or "bye")  # "hi" (first is truthy)
print(0 or "" or None)  # None (all falsy → returns the last value)
print(0 or "" or 42)  # 42 (first truthy value)

# If the user doesn't enter a name, use "Guest"
username = input("Enter name: ") or "Guest"
print(f"Hello, {username}")

# Set a default value if the configuration is missing
config = {}
db_host = config.get("host") or "localhost"
db_port = config.get("port") or 5432

# Bug: 0 is also falsy, so the default is applied
count = 0
result = count or 10  # 10 (should be 0)

# Fix: Explicit comparison
result = count if count is not None else 10  # 0

# Use `and` for conditional execution (alternative to `if`)
data = [1, 2, 3]
data and print(f"Data has {len(data)} items")  # Prints

empty = []
empty and print("This won't print")  # Doesn't print (empty list = falsy)

# Safe attribute access
user = {"name": "Hoon", "address": None}

# If `address` is None, don't call `.get()`
city = user.get("address") and user["address"].get("city")
print(city)  # None (and stops at None)

def is_valid_user(user_id):
    """DB lookup — slow operation"""
    print(f"Querying DB for user {user_id}...")
    return user_id > 0

def has_permission(user_id, action):
    """Permission check — even slower operation"""
    print(f"Checking permission for {action}...")
    return True

# Good: Checks the faster condition first
user_id = -1
if user_id > 0 and is_valid_user(user_id) and has_permission(user_id, "read"):
    print("Access granted")
# Output: (Nothing printed — `user_id > 0` is False, so the DB is not queried)

# Bad: Checks the slower condition first
if is_valid_user(user_id) and user_id > 0:
    print("Access granted")
# Output: "Querying DB for user -1..." (Unnecessary DB query)

# Indexing an empty list causes an error
items = []

# Bad: Causes an IndexError
# if items[0] > 10:

# Good: Checks if the list is empty first
if items and items[0] > 10:
    print("First item is large")
# `items` is falsy (empty list), so `items[0]` is not executed

def check_permission(user):
    print(f"Checking permission for {user['name']}")
    return user.get("role") == "admin"

def validate_input(data):
    print(f"Validating: {data}")
    return len(data) > 0

user = {"name": "Hoon", "role": "admin"}
data = "hello"

if check_permission(user) or validate_input(data):
    print("Granted")

# Output:
# Checking permission for Hoon
# Granted
# → `validate_input` is not executed! (print statement is skipped)

// JavaScript — same behavior
const name = userInput || "Guest";
const port = config.port || 3000;

// JavaScript ES2020: ?? (Nullish Coalescing)
const count = 0 ?? 10;  // 0 (?? only checks for null/undefined)
const count2 = 0 || 10;  // 10 (|| checks for all falsy values)

# Python doesn't have the ?? operator
# Instead, use explicit comparison
count = 0
result = count if count is not None else 10  # 0

# `not` doesn't use short-circuiting; it's a simple inversion
print(not True)  # False
print(not 0)  # True
print(not "")  # True
print(not "hello")  # False

# Precedence in complex conditions
# not > and > or
print(not True or False)  # False (not True → False, False or False → False)
print(not (True or False))  # False (True or False → True, not True → False)

# Use parentheses explicitly for readability
if (age >= 18) and (not is_banned):
    print("Access allowed")