9. ブール論理で条件を組み合わせる

# 両方の条件が True でなければならない
age = 25
has_license = True
 
can_rent_car = age >= 21 and has_license
print(can_rent_car)  # Output: True
 
# どちらかの条件が False なら、結果は False
age = 18
can_rent_car = age >= 21 and has_license
print(can_rent_car)  # Output: False

# 少なくとも 1 つの条件が True でなければならない
is_weekend = True
is_holiday = False
 
can_sleep_in = is_weekend or is_holiday
print(can_sleep_in)  # Output: True
 
# 両方の条件が False
is_weekend = False
is_holiday = False
can_sleep_in = is_weekend or is_holiday
print(can_sleep_in)  # Output: False

# 学生 OR シニアなら割引を受けられる
age = 68
is_student = False
 
gets_discount = is_student or age >= 65
print(f"Eligible for discount: {gets_discount}")  # Output: Eligible for discount: True
 
# 別の顧客
age = 30
is_student = False
gets_discount = is_student or age >= 65
print(f"Eligible for discount: {gets_discount}")  # Output: Eligible for discount: False

is_raining = False
is_sunny = not is_raining
print(is_sunny)  # Output: True
 
is_raining = True
is_sunny = not is_raining
print(is_sunny)  # Output: False

# ファイルが空ではないかどうかをチェックする
file_size = 0
is_empty = file_size == 0
is_not_empty = not is_empty
print(f"File has content: {is_not_empty}")  # Output: File has content: False
 
# ユーザーがログインしていないかどうかをチェックする
is_logged_in = False
needs_login_prompt = not is_logged_in
print(f"Show login prompt: {needs_login_prompt}")  # Output: Show login prompt: True

# オンラインストア: 注文が $50 以上 OR プレミアム会員なら送料無料
# さらに在庫があること
order_total = 45.00
is_premium = True
in_stock = True
 
gets_free_shipping = (order_total >= 50 or is_premium) and in_stock
print(f"Free shipping: {gets_free_shipping}")  # Output: Free shipping: True

# ユーザーが管理者なら管理パネルにアクセスできる
# そして（社内ネットワーク上にいる OR VPN を使っている）
is_admin = True
on_internal_network = False
using_vpn = True
 
can_access_admin = is_admin and (on_internal_network or using_vpn)
print(f"Can access admin panel: {can_access_admin}")  # Output: Can access admin panel: True

# かっこがない場合、優先順位が順序を決める
result = True or False and False
print(result)  # Output: True
 
# Python がこれを評価する方法:
# Step 1: False and False → False（and は or より優先順位が高い）
# Step 2: True or False → True

is_weekend = False
is_holiday = True
has_work = True
 
# 式: not has_work or is_weekend and is_holiday
free_time = not has_work or is_weekend and is_holiday
 
# 評価順序:
# Step 1: not has_work → not True → False
# Step 2: is_weekend and is_holiday → False and True → False
# Step 3: False or False → False
print(f"Has free time: {free_time}")  # Output: Has free time: False

# かっこがないと曖昧
result = True or False and False
print(result)  # Output: True
 
# かっこがあると明確 - 本当に意味したかったのはどちら？
result = (True or False) and False
print(result)  # Output: False
 
result = True or (False and False)
print(result)  # Output: True

age = 25
income = 50000
 
# 比較の周りにかっこは不要
eligible = age >= 18 and income >= 30000
print(f"Eligible for loan: {eligible}")  # Output: Eligible for loan: True
 
# Python は次のように評価する:
# Step 1: age >= 18 → True
# Step 2: income >= 30000 → True
# Step 3: True and True → True

# 単純なデモ
x = 5
result = x < 3 and x > 10
print(result)  # Output: False
 
# Python の評価:
# Step 1: x < 3 → 5 < 3 → False
# Step 2: 左側が False なので、x > 10 は評価しない
# Step 3: False を返す

# 数が割り切れるかをチェック - ゼロ除算を避ける
numerator = 100
denominator = 0
 
# これは短絡評価のおかげで安全
# denominator が 0 なら除算は発生しない
is_divisible = denominator != 0 and numerator % denominator == 0
print(f"Is divisible: {is_divisible}")  # Output: Is divisible: False
 
# 短絡評価がなければ、これはエラーになります:
# denominator = 0
# result = numerator % denominator  # ZeroDivisionError!

# 文字列プロパティを安全にチェックする
text = ""
 
# text が空ではない AND 先頭文字が大文字であるかをチェックする
# text が空なら text[0] にアクセスしないので安全
has_uppercase_start = len(text) > 0 and text[0].isupper()
print(f"Starts with uppercase: {has_uppercase_start}")  # Output: Starts with uppercase: False
 
# 長さチェックなしでこれを試すと:
# text = ""
# result = text[0].isupper()  # IndexError: string index out of range

# 単純なデモ
x = 15
result = x > 10 or x < 5
print(result)  # Output: True
 
# Python の評価:
# Step 1: x > 10 → 15 > 10 → True
# Step 2: 左側が True なので、x < 5 は評価しない
# Step 3: True を返す

# リスト要素へ安全にアクセスする
numbers = [1, 2, 3]
index = 5
 
# アクセス前に index が有効かどうかをチェックする
is_valid = index < len(numbers) and numbers[index] > 0
print(f"Valid and positive: {is_valid}")  # Output: Valid and positive: False
 
# 短絡がなければ、これはクラッシュします:
# is_valid = numbers[index] > 0  # IndexError!

# フォーム検証 - 最初のエラーで止める
email = "user@example.com"
password = "pass"
age = 25
 
# 失敗しやすい順に各要件をチェックする
valid_form = (
    len(email) > 0 and              # Quick check
    "@" in email and                # Quick check
    len(password) >= 8 and          # Quick check
    age >= 18                       # Quick check
)
print(f"Form valid: {valid_form}")  # Output: Form valid: False
# Stops at password length check, doesn't evaluate age

# truthy をデモする
if "hello":
    print("Non-empty strings are truthy")  # Output: Non-empty strings are truthy
 
if 0:
    print("This won't print")  # Zero is falsy
else:
    print("Zero is falsy")  # Output: Zero is falsy
 
if [1, 2, 3]:
    print("Non-empty lists are truthy")  # Output: Non-empty lists are truthy

# and は最初の falsy 値、またはすべて truthy なら最後の値を返す
result = 5 and 10
print(result)  # Output: 10
 
result = 0 and 10
print(result)  # Output: 0
 
result = "hello" and "world"
print(result)  # Output: world
 
result = "" and "world"
print(result)  # Output: (empty string)
 
result = None and "world"
print(result)  # Output: None

# Example 1: Both truthy
result = 5 and 10
# Step 1: 5 is truthy, so evaluate right side
# Step 2: Return right side value: 10
print(result)  # Output: 10
 
# Example 2: Left is falsy
result = 0 and 10
# Step 1: 0 is falsy, so return it immediately
# Step 2: Don't evaluate right side
print(result)  # Output: 0
 
# Example 3: Both truthy strings
result = "hello" and "world"
# Step 1: "hello" is truthy, so evaluate right side
# Step 2: Return right side value: "world"
print(result)  # Output: world

# or は最初の truthy 値、またはすべて falsy なら最後の値を返す
result = 5 or 10
print(result)  # Output: 5
 
result = 0 or 10
print(result)  # Output: 10
 
result = "" or "default"
print(result)  # Output: default
 
result = "hello" or "world"
print(result)  # Output: hello
 
result = None or 0
print(result)  # Output: 0

# Example 1: Left is truthy
result = 5 or 10
# Step 1: 5 is truthy, so return it immediately
# Step 2: Don't evaluate right side
print(result)  # Output: 5
 
# Example 2: Left is falsy
result = 0 or 10
# Step 1: 0 is falsy, so evaluate right side
# Step 2: Return right side value: 10
print(result)  # Output: 10
 
# Example 3: Both falsy
result = None or 0
# Step 1: None is falsy, so evaluate right side
# Step 2: Return right side value: 0 (even though it's also falsy)
print(result)  # Output: 0

# デフォルト付きのユーザー設定
user_theme = ""  # ユーザーがテーマを設定していない
theme = user_theme or "light"
print(f"Theme: {theme}")  # Output: Theme: light
 
user_theme = "dark"
theme = user_theme or "light"
print(f"Theme: {theme}")  # Output: Theme: dark
 
# 設定値
max_retries = None  # 未設定
retries = max_retries or 3
print(f"Retries: {retries}")  # Output: Retries: 3
 
max_retries = 5
retries = max_retries or 3
print(f"Retries: {retries}")  # Output: Retries: 5

# 3 つの演算子すべてをデモする
print(5 and 10)           # Output: 10 (both truthy, return last)
print(0 and 10)           # Output: 0 (first falsy, return it)
print(5 or 10)            # Output: 5 (first truthy, return it)
print(0 or 10)            # Output: 10 (first falsy, evaluate second)
print(not 5)              # Output: False (5 is truthy, not returns boolean)
print(not 0)              # Output: True (0 is falsy, not returns boolean)
print(not "")             # Output: True (empty string is falsy)
print(not "hello")        # Output: False (non-empty string is truthy)