Python利用元类打造更优雅的类属性访问机制

from functools import lru_cache


class Meta(type):
    @property
    def test(cls) -> str:
        """测试属性"""
        if not hasattr(cls, '__test__'):
            cls.__test__ = 'test'
        return cls.__test__

    @test.setter
    def test(cls, value: str):
        cls.__test__ = value

    @property
    @lru_cache(maxsize=1)
    def single(cls):
        """单例属性"""
        return cls()


class MyClass(metaclass=Meta):
    single: 'MyClass'  # 类型注解

    def __init__(self):
        print('init')
        self.abc = 'abc'


# 使用方式
MyClass.test = 'test2'  # 设置属性
print(MyClass.test)     # 输出: test2
print(MyClass.single.abc)  # 输出: abc

# 访问方式：类名.single.方法()
UserService.single.get_user(123)
ConfigService.single.get('database.host')

from functools import lru_cache
from typing import TypeVar, Generic


class Meta(type):
    """服务端元类"""

    @property
    @lru_cache(maxsize=None)
    def single(cls):
        """获取单例实例（延迟创建）"""
        return cls()


class Service(metaclass=Meta):
    """服务基类"""
    pass


# 定义用户服务
class UserService(Service):
    single: 'UserService'  # IDE 类型提示

    def __init__(self):
        # 模拟初始化（如连接数据库）
        print('UserService 初始化')
        self._cache = {}

    def get_user(self, user_id: int) -> dict:
        """获取用户信息"""
        if user_id not in self._cache:
            self._cache[user_id] = {'id': user_id, 'name': f'User_{user_id}'}
        return self._cache[user_id]


# 定义配置服务
class ConfigService(Service):
    single: 'ConfigService'

    def __init__(self):
        print('ConfigService 初始化')
        self._config = {'database': {'host': 'localhost', 'port': 3306}}

    def get(self, key: str, default=None):
        """获取配置值"""
        keys = key.split('.')
        value = self._config
        for k in keys:
            if isinstance(value, dict) and k in value:
                value = value[k]
            else:
                return default
        return value


# 使用方式
if __name__ == '__main__':
    # 首次访问时创建实例
    user = UserService.single.get_user(123)
    print(user)

    # 再次访问返回同一实例
    user2 = UserService.single.get_user(456)

    # 配置服务
    host = ConfigService.single.get('database.host')
    print(f'数据库地址: {host}')

class UserService(Service):
    single: 'UserService'  # 类型注解，告诉 IDE single 返回 UserService

from typing import Protocol
class IBusiness(Protocol):
    '''业务逻辑接口'''
    def start(self, url: str) -> None:
        '''开始爬取操作. 在新线程中执行.'''
    def stop(self) -> None:
        '''停止爬取链接'''

class UserService(Service):
    single: 'IBusiness'  # 类型注解，告诉 IDE single 返回 UserService