Python中的raise关键字详解

raise [异常类型[(参数)]]

raise [异常类型[(参数)]] [from 原因]

# 参数校验场景
def calculate_square(n):
    if not isinstance(n, (int, float)):
        raise TypeError("必须传入数值类型")
    return n ​**​ 2

# 调用示例
calculate_square("5")  # 触发 TypeError

import json

try:
    config = json.load(open('config.json'))
except FileNotFoundError as fnf_error:
    raise RuntimeError("配置文件加载失败") from fnf_error

# 错误输出显示关联关系
# RuntimeError: 配置文件加载失败
# The above exception was the direct cause of...

class NetworkTimeout(Exception):
"""自定义网络超时异常"""
	def __init__(self, host, timeout):
	    self.host = host
	    self.timeout = timeout
	    super().__init__(f"连接 {host} 超时（{timeout}s）")

# 触发自定义异常
if response_time > 30:
	raise NetworkTimeout("api.example.com", 30)

def deprecated_feature():
    raise "该功能已废弃"  # ❌ 错误！必须抛出 Exception 实例

# 正确做法
def deprecated_feature():
    raise DeprecationWarning("该功能已废弃")

try:
    raise ValueError("无效输入", 404, {"detail": "ID不合法"})
except ValueError as e:
    print(e.args)  # ('无效输入', 404, {'detail': 'ID不合法'})

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

def fetch_data(url):
    response = requests.get(url)
    if 400 <= response.status_code < 500:
        raise ClientError(response.status_code, response.text)
    elif response.status_code >= 500:
        raise ServerError(response.status_code)
    return response.json()

# 不推荐
raise ValueError("错误发生")

# 推荐格式
raise ValueError(f"参数 {param} 的值 {value} 超出有效范围（允许范围：{min}~{max}）")

# 显示原始异常原因
raise ParsingError from original_error

# 打印完整堆栈
import traceback
try:
    risky_call()
except:
    traceback.print_exc()
    raise  # 重新抛出

def validate_user(user):
    if not user.get('username'):
        raise ValueError("用户名必填")
    if len(user['password']) < 8:
        raise SecurityError("密码至少8位")
    if not re.match(r"[^@]+@[^@]+\.[^@]+", user['email']):
        raise FormatError("邮箱格式无效")
    return True

class Transaction:
    def __enter__(self):
        if not self.conn.is_valid():
            raise ConnectionError("数据库连接失效")
        return self
    
    def __exit__(self, exc_type, exc_val, exc_tb):
        if exc_type:
            self.rollback()
            raise TransactionError("事务执行失败") from exc_val
        self.commit()