Python主动抛出异常的各种用法和场景分析

raise 异常类型(错误信息)

def divide(a, b):
    if b == 0:
        # ValueError是内置的异常类型，就不需要自己定义了
        raise ValueError("除数不能为零")
    return a / b

try:
    result = divide(10, 0)
except ValueError as e:
    print(f"捕获到错误: {e}")

def get_element(lst, index):
    if index >= len(lst):
        # IndexError错误类型因为他原本就有所以不用class定义
        raise IndexError("索引超出列表范围")
    return lst[index]

# 使用
try:
    get_element([1, 2, 3], 5)
except IndexError as e:
    print(e)  # 输出：索引超出列表范围

try:
    10 / 0
except ZeroDivisionError:
    print("发生了除以零错误，记录日志后重新抛出")
    raise  # 重新抛出相同的异常

def process_file(filename):
    try:
        with open(filename) as f:
            return f.read()
    except IOError as e:
        raise RuntimeError("文件处理失败") from e

try:
    process_file("nonexistent.txt")
except RuntimeError as e:
    print(f"主错误: {e}")
    print(f"原始原因: {e.__cause__}")  # 访问原始异常

# 自定义一个异常类型（InvalidEmailError），以及异常消息
class InvalidEmailError(Exception):
    """当电子邮件格式无效时抛出"""
    pass

def send_email(email):
    if "@" not in email:
        raise InvalidEmailError(f"无效的邮箱地址: {email}")
    # 发送邮件逻辑...

try:
    send_email("userexample.com")  # 缺少@符号
except InvalidEmailError as e:
    print(f"邮件发送失败: {e}")

class TemperatureError(Exception):
    def __init__(self, temp, min_temp, max_temp):
        self.temp = temp
        self.min_temp = min_temp
        self.max_temp = max_temp
        super().__init__(f"温度{temp}超出范围({min_temp}-{max_temp})")

def check_temperature(temp):
    if not (0 <= temp <= 100):
        raise TemperatureError(temp, 0, 100)
    print("温度正常")

try:
    check_temperature(-5)
except TemperatureError as e:
    print(f"错误温度: {e.temp}, 允许范围: {e.min_temp}-{e.max_temp}")

def process_age(age):
    if not isinstance(age, int):
        raise TypeError("年龄必须是整数")
    if age < 0:
        raise ValueError("年龄不能为负数")
    if age < 18:
        print("未成年人")
    else:
        print("成年人")

# 测试
for age in [15, 25, -3, "20"]:
    try:
        process_age(age)
    except (TypeError, ValueError) as e:
        print(f"无效输入: {e}")

def calculate_average(numbers):
    assert len(numbers) > 0, "数字列表不能为空"
    return sum(numbers) / len(numbers)

# 等同于
def calculate_average(numbers):
    if len(numbers) == 0:
        raise ValueError("数字列表不能为空")
    return sum(numbers) / len(numbers)

def create_user(username, email):
    if not username:
        raise ValueError("用户名不能为空")
    if len(username) < 3:
        raise ValueError("用户名至少需要3个字符")
    if "@" not in email:
        raise ValueError("无效的邮箱格式")
    
    print(f"创建用户: {username}, 邮箱: {email}")

try:
    create_user("ab", "invalid-email")
except ValueError as e:
    print(f"用户创建失败: {e}")

class DatabaseError(Exception):
    pass

class ConnectionError(DatabaseError):
    pass

class QueryError(DatabaseError):
    pass

def execute_query(query):
    if not query.startswith("SELECT"):
        raise QueryError("只支持SELECT查询")
    # 模拟连接失败
    if "fail" in query:
        raise ConnectionError("数据库连接失败")
    print(f"执行查询: {query}")

queries = ["SELECT * FROM users", "UPDATE users", "SELECT fail"]
for query in queries:
    try:
        execute_query(query)
    except ConnectionError as e:
        print(f"连接问题: {e}")
    except QueryError as e:
        print(f"查询错误: {e}")