Python デコレータ徹底解説：基礎から応用までわかりやすく解説！

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# デコレータの定義
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def my_decorator(func):
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    def wrapper():
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        print("処理開始")
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        func()
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        print("処理終了")
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    return wrapper
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# デコレータを適用
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@my_decorator
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def my_function():
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    print("メインの処理")
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my_function()

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def my_decorator(func):
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    def wrapper(*args, **kwargs):
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        print("処理開始")
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        result = func(*args, **kwargs)
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        print(result)
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        print("処理終了")
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        return result
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    return wrapper
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@my_decorator
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def add(a, b):
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    return a + b
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add(3, 5)

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def decorator1(func):
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    def wrapper(*args, **kwargs):
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        print("デコレータ1実行")
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        return func(*args, **kwargs)
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    return wrapper
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def decorator2(func):
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    def wrapper(*args, **kwargs):
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        print("デコレータ2実行")
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        return func(*args, **kwargs)
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    return wrapper
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@decorator1
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@decorator2
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def say_hello():
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    print("Hello!")
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say_hello()

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def class_decorator(cls):
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    class NewClass(cls):
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        def new_method(self):
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            return "追加メソッド"
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    return NewClass
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@class_decorator
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class MyClass:
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    def original_method(self):
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        return "元のメソッド"
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obj = MyClass()
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print(obj.original_method())
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print(obj.new_method())

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import functools
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def log_decorator(func):
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    @functools.wraps(func)
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    def wrapper(*args, **kwargs):
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        print(f"関数 {func.__name__} を実行します")
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        return func(*args, **kwargs)
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    return wrapper
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@log_decorator
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def greet(name):
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    print(f"こんにちは、{name}！")
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greet("太郎")

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import time
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def timer_decorator(func):
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    def wrapper(*args, **kwargs):
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        start_time = time.time()
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        result = func(*args, **kwargs)
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        end_time = time.time()
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        print(f"実行時間: {end_time - start_time} 秒")
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        return result
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    return wrapper
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@timer_decorator
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def slow_function():
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    time.sleep(2)
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    print("処理が完了しました")
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slow_function()

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from functools import lru_cache
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@lru_cache(maxsize=5)
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def fibonacci(n):
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    if n < 2:
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        return n
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    return fibonacci(n-1) + fibonacci(n-2)
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print(fibonacci(10))

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def auth_decorator(func):
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    def wrapper(user):
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        if user != "admin":
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            print("アクセス拒否")
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            return
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        return func(user)
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    return wrapper
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@auth_decorator
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def secret_function(user):
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    print("機密情報を表示")
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print("▼guestの場合")
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secret_function("guest")
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print("▼adminの場合")
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secret_function("admin")

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def singleton(cls):
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    instances = {}
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    def get_instance(*args, **kwargs):
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        if cls not in instances:
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            instances[cls] = cls(*args, **kwargs)
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        return instances[cls]
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    return get_instance
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@singleton
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class Database:
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    def __init__(self):
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        print("データベース接続")
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db1 = Database()
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db2 = Database()
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print(db1 is db2)  # True