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面试-python单例模式实现

news 2025/8/3 11:55:16

概念:
一个对象只能最多存在一个实例

优点:
节省资源空间

缺点:
多线程失效，需要加锁解决

两种实现方式:

需要用到的知识点
1.单例模式思想

2.装饰器

3.类对象
4.__new__方法

4.with语句
5.多线程资源竞争使单例模式失效，导致脏读，使用锁解决

# 方式1：装饰器实现 非线程安全
def singleton(cls):_instances = {}def wrapper(*args, **kwargs):if cls not in _instances:_instances[cls] = cls(*args, **kwargs)return _instances[cls]return wrapper
@singleton
class ConfigManager:def __init__(self):self.settings = {}

# 方式1：装饰器实现 线程安全
import threading
def singleton(cls):__instances = {}__lock = threading.Lock()def wrapper(*args, **kwargs):with __lock:if cls not in _instances:_instances[cls] = cls(*args, **kwargs)return _instances[cls]return wrapper@singleton
class ConfigManager:def __init__(self):self.settings = {}

# 方式2：__new__方法重写    重点++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
class CacheManager:_instance = Nonedef __new__(cls):if not cls._instance:cls._instance = super().__new__(cls)cls._instance._cache = {}return cls._instance

# 方式2：线程安全版（带锁）
from threading import Lockclass ThreadSafeSingleton:_instance = None_lock = Lock()def __new__(cls):if not cls._instance:with cls._lock:if not cls._instance:cls._instance = super().__new__(cls)return cls._instance