try-except-else-finally如何协同工作？else块容易被忽略的关键作用是什么？

def read_file(filename):
    try:
        f = open(filename, 'r')
        data = f.read()
    except FileNotFoundError:
        print(f"Error: File '{filename}' not found.")
        return None
    except IOError:
        print(f"Error: Could not read file '{filename}'.")
        return None
    else:
        print(f"File '{filename}' read successfully.")
        return data
    finally:
        if 'f' in locals() and hasattr(f, 'close'): # 确保文件对象存在且有close方法
            f.close()
            print(f"File '{filename}' closed.")

# 使用示例
content = read_file("my_file.txt")
if content:
    print("File content:", content)

def read_nested_file(config_file):
    try:
        # 读取配置文件
        with open(config_file, 'r') as f:
            nested_file_path = f.readline().strip()

        try:
            # 读取嵌套文件
            with open(nested_file_path, 'r') as nested_f:
                nested_content = nested_f.read()
        except FileNotFoundError:
            print(f"Error: Nested file '{nested_file_path}' not found.")
            return None
        except IOError:
            print(f"Error: Could not read nested file '{nested_file_path}'.")
            return None
        else:
            print(f"Nested file '{nested_file_path}' read successfully.")
            return nested_content
        finally:
            print("Inner finally block executed.")

    except FileNotFoundError:
        print(f"Error: Config file '{config_file}' not found.")
        return None
    except IOError:
        print(f"Error: Could not read config file '{config_file}'.")
        return None
    else:
        print(f"Config file '{config_file}' read successfully.")
    finally:
        print("Outer finally block executed.")

# 使用示例
nested_file_content = read_nested_file("config.txt")
if nested_file_content:
    print("Nested file content:", nested_file_content)

import threading
import time
import logging

logging.basicConfig(level=logging.DEBUG,
                    format='(%(threadName)-9s) %(message)s',)

class Worker(threading.Thread):
    def __init__(self, lock, filename):
        super().__init__()
        self.lock = lock
        self.filename = filename

    def run(self):
        logging.debug('Starting')
        try:
            with self.lock:
                logging.debug('Lock acquired')
                with open(self.filename, 'w') as f:
                    f.write("Hello, world!\n")
                    time.sleep(2)  # 模拟一些耗时操作
                    raise ValueError("Simulated error") # 模拟错误
        except FileNotFoundError:
            logging.error(f"File '{self.filename}' not found.")
        except ValueError as e:
            logging.error(f"ValueError: {e}")
        except Exception as e:
            logging.error(f"An unexpected error occurred: {e}")
        finally:
            if self.lock.locked():
                self.lock.release()
                logging.debug('Lock released')
            logging.debug('Finishing')

# 创建一个锁
lock = threading.Lock()

# 创建并启动线程
worker1 = Worker(lock, "file1.txt")
worker2 = Worker(lock, "file1.txt") # 故意使用相同的文件名，模拟资源竞争
worker1.start()
worker2.start()

worker1.join()
worker2.join()

logging.debug('All done')

def process_data(data):
    try:
        # 步骤 1: 验证数据
        validated_data = validate(data)

        # 步骤 2: 处理数据 (只有在数据验证成功后才应该执行)
        result = process(validated_data)

        # 步骤 3: 保存结果
        save_result(result)

    except ValidationError as e:
        print(f"Validation error: {e}")
    except ProcessingError as e:
        print(f"Processing error: {e}")
    except Exception as e:
        print(f"An unexpected error occurred: {e}")
    finally:
        print("Cleanup operations")

def process_data(data):
    try:
        # 步骤 1: 验证数据
        validated_data = validate(data)
    except ValidationError as e:
        print(f"Validation error: {e}")
    except Exception as e:
        print(f"An unexpected error occurred during validation: {e}") # 更具体的错误信息
    else:
        try:
            # 步骤 2: 处理数据 (只有在数据验证成功后才应该执行)
            result = process(validated_data)

            # 步骤 3: 保存结果
            save_result(result)
        except ProcessingError as e:
            print(f"Processing error: {e}")
        except Exception as e:
            print(f"An unexpected error occurred during processing or saving: {e}") # 更具体的错误信息
    finally:
        print("Cleanup operations")