python中类装饰器的实现示例

@decorator
class MyClass:
    pass

class MyClass:
    pass

MyClass = decorator(MyClass)

def decorator(cls):
    # 修改类或返回一个新的类
    return cls

def add_class_attribute(attr_name, attr_value):
    def decorator(cls):
        setattr(cls, attr_name, attr_value)
        return cls
    return decorator

@add_class_attribute('new_attribute', 42)
class MyClass:
    pass

print(MyClass.new_attribute)  # 输出 42

def add_instance_method(method_name, method):
    def decorator(cls):
        setattr(cls, method_name, method)
        return cls
    return decorator

def greet(self):
    return f"Hello, my name is {self.name}"

@add_instance_method('greet', greet)
class Person:
    def __init__(self, name):
        self.name = name

person = Person("Alice")
print(person.greet())  # 输出 "Hello, my name is Alice"

import logging

def log_initialization(cls):
    original_init = cls.__init__

    def new_init(self, *args, **kwargs):
        logging.info(f"Initializing {cls.__name__} with args={args} and kwargs={kwargs}")
        original_init(self, *args, **kwargs)

    cls.__init__ = new_init
    return cls

@log_initialization
class MyClass:
    def __init__(self, name):
        self.name = name

obj = MyClass("Test")
# 日志输出: INFO:root:Initializing MyClass with args=('Test',) and kwargs={}

def singleton(cls):
    instance = None

    def wrapper(*args, **kwargs):
        nonlocal instance
        if instance is None:
            instance = cls(*args, **kwargs)
        return instance

    return wrapper

@singleton
class MyClass:
    def __init__(self, name):
        self.name = name

obj1 = MyClass("Alice")
obj2 = MyClass("Bob")

print(obj1 is obj2)  # 输出 True
print(obj1.name)  # 输出 Alice
print(obj2.name)  # 输出 Alice

def validate_attributes(**validations):
    def decorator(cls):
        original_init = cls.__init__

        def new_init(self, *args, **kwargs):
            original_init(self, *args, **kwargs)
            for attr_name, validation_func in validations.items():
                value = getattr(self, attr_name)
                if not validation_func(value):
                    raise ValueError(f"Invalid value for {attr_name}: {value}")

        cls.__init__ = new_init
        return cls
    return decorator

def is_positive(value):
    return value > 0

@validate_attributes(age=is_positive)
class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

person = Person("Alice", 30)
# person = Person("Alice", -1)  # 抛出 ValueError: Invalid value for age: -1