python语法笔记之Python raise语句用法详解

raise [异常类型] [异常信息]

raise

raise ExceptionType

raise ExceptionType("错误信息")

raise ExceptionType("错误信息") from 原始异常

def divide(a, b):
    if b == 0:
        raise ValueError("除数不能为零")
    return a / b

def process_data(data):
    if not data:
        raise ValueError("数据不能为空")
    if len(data) < 10:
        raise ValueError("数据长度不足")

def withdraw_money(account, amount):
    if amount <= 0:
        raise ValueError("取款金额必须大于零")
    if amount > account.balance:
        raise InsufficientFundsError("余额不足")

try:
    # 可能出错的代码
    result = risky_operation()
except Exception as e:
    # 记录日志
    logger.error(f"操作失败: {e}")
    # 重新抛出异常
    raise

class CustomError(Exception):
    """自定义异常基类"""
    pass

class ValidationError(CustomError):
    """验证错误"""
    pass

class BusinessError(CustomError):
    """业务逻辑错误"""
    pass

class DatabaseError(Exception):
    def __init__(self, message, error_code=None, table=None):
        super().__init__(message)
        self.error_code = error_code
        self.table = table

# 使用示例
raise DatabaseError("连接失败", error_code="DB001", table="users")

try:
    # 尝试读取文件
    with open("nonexistent.txt") as f:
        data = f.read()
except FileNotFoundError as e:
    # 重新抛出异常，保留原始信息
    raise RuntimeError("无法处理文件") from e

# 不好的做法
raise ValueError("错误")

# 好的做法
raise ValueError("年龄必须是正整数，当前值: 25.5")

def validate_user(user):
    errors = []
    
    if not user.name:
        errors.append("用户名不能为空")
    if user.age < 0:
        errors.append("年龄不能为负数")
    if user.email and '@' not in user.email:
        errors.append("邮箱格式不正确")
    
    if errors:
        raise ValidationError(f"用户验证失败: {'; '.join(errors)}")

try:
    result = external_api_call()
except requests.RequestException as e:
    raise BusinessError("外部服务调用失败") from e

def safe_operation():
    try:
        # 可能出错的代码
        result = risky_function()
        return result
    except SpecificError as e:
        # 处理特定异常
        logger.warning(f"特定错误: {e}")
        # 重新抛出
        raise
    except Exception as e:
        # 处理其他异常
        logger.error(f"未知错误: {e}")
        # 转换为自定义异常
        raise BusinessError("操作失败") from e

def level3():
    raise ValueError("这是第三层的错误")

def level2():
    try:
        level3()
    except ValueError as e:
        raise RuntimeError("第二层捕获并重新抛出") from e

def level1():
    try:
        level2()
    except RuntimeError as e:
        print(f"第一层捕获: {e}")
        print(f"原始错误: {e.__cause__}")

class ErrorReporter:
    def report_error(self, error, context=None):
        error_info = {
            "type": type(error).__name__,
            "message": str(error),
            "context": context,
            "timestamp": datetime.now().isoformat()
        }
        # 上报错误信息
        self.send_to_monitoring_system(error_info)

def monitored_function():
    try:
        # 业务逻辑
        result = business_logic()
        return result
    except Exception as e:
        # 上报错误
        error_reporter.report_error(e, {"function": "monitored_function"})
        # 重新抛出异常
        raise

class ErrorLevel:
    CRITICAL = 1
    HIGH = 2
    MEDIUM = 3
    LOW = 4

def handle_error_with_level(error, level):
    if level == ErrorLevel.CRITICAL:
        # 立即上报并停止服务
        report_critical_error(error)
        raise SystemExit(1)
    elif level == ErrorLevel.HIGH:
        # 上报并记录
        report_high_priority_error(error)
        raise
    else:
        # 仅记录
        log_error(error)
        raise

# 不好的做法：过度使用异常
def get_user_age(user):
    if not user:
        raise ValueError("用户对象不能为空")
    if not hasattr(user, 'age'):
        raise AttributeError("用户对象没有age属性")
    if user.age is None:
        raise ValueError("用户年龄不能为空")
    return user.age

# 好的做法：合理使用异常
def get_user_age(user):
    if not user or not hasattr(user, 'age') or user.age is None:
        raise ValueError("无法获取用户年龄")
    return user.age

# 不好的做法
try:
    # 业务逻辑
    pass
finally:
    # 清理资源
    cleanup()
    raise RuntimeError("清理失败")  # 这会覆盖原始异常

# 正确的做法
try:
    # 业务逻辑
    pass
except Exception as e:
    # 记录原始异常
    logger.error("原始错误", exc_info=True)
    # 抛出新的异常
    raise CustomError("处理失败") from e

import traceback

try:
    # 可能出错的代码
    pass
except Exception as e:
    # 打印完整的堆栈跟踪
    print("异常信息:", str(e))
    print("堆栈跟踪:")
    traceback.print_exc()
    raise

def format_exception_info(error):
    return {
        "type": type(error).__name__,
        "message": str(error),
        "traceback": traceback.format_exc(),
        "args": error.args
    }