Python __del__方法与对象复活：深入理解终结器行为及替代方案

cache = []

class Temp:
    def __init__(self) -> None:
        self.cache = True
        print(f"Temp object created, cache_flag: {self.cache}")

    def __del__(self) -> None:
        print('Running del')
        if self.cache:
            # 在 __del__ 中重新创建对 self 的引用，实现对象复活
            cache.append(self)
            print("Object resurrected and added to cache.")

def main():
    temp = Temp()
    print(f"Inside main, temp.cache: {temp.cache}")
    # temp 离开作用域，引用计数降为0，__del__ 预期被调用

main()
print("Main function finished.")
if cache:
    print(f"Cache contains resurrected object. cache[0].cache: {cache[0].cache}")
print("Program end.")

Temp object created, cache_flag: True
Inside main, temp.cache: True
Running del
Object resurrected and added to cache.
Main function finished.
Cache contains resurrected object. cache[0].cache: True
Program end.

class ManagedResource:
    def __init__(self, name):
        self.name = name
        print(f"Resource '{self.name}' initialized.")

    def __enter__(self):
        print(f"Resource '{self.name}' acquired.")
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        print(f"Resource '{self.name}' released.")
        if exc_type:
            print(f"An exception occurred: {exc_val}")
        return False # 不抑制异常

# 使用上下文管理器
print("--- Using Context Manager ---")
with ManagedResource("FileHandler") as res:
    print(f"Working with {res.name}")
    # 模拟操作
print("--- Context Manager Finished ---")

# 模拟异常情况
print("\n--- Using Context Manager with Exception ---")
try:
    with ManagedResource("DatabaseConnection") as db:
        print(f"Connecting to {db.name}")
        raise ValueError("Simulated database error")
except ValueError as e:
    print(f"Caught exception outside context: {e}")
print("--- Context Manager with Exception Finished ---")

--- Using Context Manager ---
Resource 'FileHandler' initialized.
Resource 'FileHandler' acquired.
Working with FileHandler
Resource 'FileHandler' released.
--- Context Manager Finished ---

--- Using Context Manager with Exception ---
Resource 'DatabaseConnection' initialized.
Resource 'DatabaseConnection' acquired.
Connecting to DatabaseConnection
Resource 'DatabaseConnection' released.
An exception occurred: Simulated database error
Caught exception outside context: Simulated database error
--- Context Manager with Exception Finished ---

import atexit

class DataSaver:
    def __init__(self, data_source):
        self.data = data_source
        self.is_saved = False
        print(f"DataSaver initialized for {self.data}")
        # 注册清理函数
        atexit.register(self.save_data_on_exit)

    def save_data_on_exit(self):
        if not self.is_saved:
            print(f"Saving data '{self.data}' to persistent storage via atexit...")
            # 模拟数据保存操作
            self.is_saved = True
        else:
            print(f"Data '{self.data}' already saved.")

# 创建一个DataSaver对象
saver = DataSaver("User Preferences")
# 可以在程序运行期间进行其他操作
print("Program running...")

# 模拟程序即将退出
# 此时，atexit注册的save_data_on_exit会被调用

DataSaver initialized for User Preferences
Program running...
Saving data 'User Preferences' to persistent storage via atexit...