Python raise语句详解 - 主动抛出异常与异常链

# raise的基本语法形式
raise Exception              # 抛出异常类
raise Exception("错误信息")   # 抛出异常实例
raise                        # 重新抛出当前异常

# 示例：参数验证
def set_age(age):
    if not isinstance(age, int):
        raise TypeError("年龄必须是整数")
    if age < 0 or age > 150:
        raise ValueError("年龄必须在0到150之间")
    print(f"年龄设置为：{age}")

# 正确调用
set_age(25)

# 触发异常
try:
    set_age(-5)
except ValueError as e:
    print(f"捕获异常：{e}")

try:
    set_age("二十五")
except TypeError as e:
    print(f"捕获异常：{e}")

import logging

logging.basicConfig(level=logging.ERROR)

def process_file(filepath):
    try:
        with open(filepath, 'r') as f:
            data = f.read()
            return int(data)
    except FileNotFoundError:
        logging.error(f"文件不存在：{filepath}")
        raise  # 重新抛出，让调用者知道发生了错误
    except ValueError:
        logging.error(f"文件内容不是有效整数")
        raise  # 重新抛出原始异常

try:
    result = process_file("nonexistent.txt")
except FileNotFoundError:
    print("调用者捕获到了重新抛出的异常")

class DatabaseError(Exception):
    pass

def save_to_database(data):
    try:
        # 模拟数据库操作
        import json
        json.loads(data)  # 可能抛出JSONDecodeError
    except Exception as e:
        # 将底层异常转换为业务异常
        raise DatabaseError(f"数据库保存失败：{e}")

try:
    save_to_database("{invalid json}")
except DatabaseError as e:
    print(f"业务层捕获：{e}")

def read_config(filepath):
    try:
        with open(filepath) as f:
            return f.read()
    except FileNotFoundError as e:
        raise ValueError("配置文件加载失败") from e

try:
    read_config("config.ini")
except ValueError as e:
    print(f"捕获的异常：{e}")
    print(f"原始异常：{e.__cause__}")
    # 输出会显示完整的异常链

class APIError(Exception):
    pass

def fetch_user(user_id):
    """模拟API调用"""
    if not isinstance(user_id, int):
        raise TypeError(f"user_id必须是整数，收到{type(user_id).__name__}")
    if user_id <= 0:
        raise ValueError(f"user_id必须大于0，收到{user_id}")
    if user_id > 10000:
        raise APIError(f"用户{user_id}不存在")
    return {"id": user_id, "name": f"User{user_id}"}

def safe_fetch_user(user_id):
    """安全的API调用包装器"""
    try:
        return fetch_user(user_id)
    except TypeError as e:
        raise APIError(f"参数错误：{e}") from e
    except ValueError as e:
        raise APIError(f"参数越界：{e}") from e

# 测试
for test_id in ["abc", -1, 99999, 42]:
    try:
        result = safe_fetch_user(test_id)
        print(f"成功：{result}")
    except APIError as e:
        print(f"API错误：{e}")
        if e.__cause__:
            print(f"  原因：{type(e.__cause__).__name__}: {e.__cause__}")

class UserService:
    def get_user(self, user_id):
        try:
            # 模拟数据库查询
            import sqlite3
            raise sqlite3.OperationalError("数据库连接失败")
        except Exception:
            # 使用from None隐藏数据库细节
            raise LookupError("用户不存在") from None

service = UserService()
try:
    service.get_user(1)
except LookupError as e:
    print(f"捕获：{e}")
    print(f"__cause__: {e.__cause__}")  # 输出: None