class MyCustomError(Exception):
    """自定义异常类示例"""
    pass

try:
    raise MyCustomError("发生了自定义错误")
except MyCustomError as e:
    print(e)

class ValidationError(Exception):
    def __init__(self, message, error_code=None):
        super().__init__(message)
        self.error_code = error_code
        self.timestamp = datetime.now()
<h1>使用示例</h1><p>from datetime import datetime</p><p>try:
raise ValidationError("用户名格式无效", error_code=400)
except ValidationError as e:
print(f"错误: {e}")
print(f"错误码: {e.error_code}")
print(f"时间: {e.timestamp}")</p>

class UsernameTooShortError(Exception):
    pass
<p>class InvalidEmailError(Exception):
pass</p><p>def register_user(username, email):
if len(username) < 3:
raise UsernameTooShortError("用户名至少需要3个字符")
if "@" not in email:
raise InvalidEmailError("邮箱格式不正确")</p><h1>调用并处理</h1><p>try:
register_user("ab", "invalid-email")
except UsernameTooShortError as e:
print("用户名问题:", e)
except InvalidEmailError as e:
print("邮箱问题:", e)</p>