backup materials and knowledge-base docs
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"""
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错误处理模式示例
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展示各种错误处理的最佳实践
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"""
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import logging
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from typing import Optional, List, Dict, Any
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from functools import wraps
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logger = logging.getLogger(__name__)
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# ============================================
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# 模式 1：具体异常捕获
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# ============================================
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def read_file(filepath: str) -> Optional[str]:
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"""
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捕获具体异常而不是宽泛的 Exception
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"""
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try:
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with open(filepath, 'r') as f:
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return f.read()
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except FileNotFoundError:
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logger.error(f"文件不存在: {filepath}")
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return None
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except PermissionError:
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logger.error(f"没有权限读取文件: {filepath}")
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return None
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except UnicodeDecodeError:
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logger.error(f"文件编码错误: {filepath}")
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return None
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# ============================================
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# 模式 2：带重试的操作
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# ============================================
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def retry_operation(max_attempts: int = 3):
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"""
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装饰器：自动重试失败的操作
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"""
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def decorator(func):
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@wraps(func)
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def wrapper(*args, **kwargs):
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for attempt in range(1, max_attempts + 1):
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try:
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return func(*args, **kwargs)
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except Exception as e:
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if attempt == max_attempts:
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logger.error(f"操作失败，已重试 {max_attempts} 次: {e}")
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raise
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logger.warning(f"操作失败，第 {attempt} 次重试...")
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return None
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return wrapper
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return decorator
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@retry_operation(max_attempts=3)
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def unstable_api_call() -> Dict[str, Any]:
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"""
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模拟不稳定的 API 调用
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"""
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import random
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if random.random() < 0.7: # 70% 失败率
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raise ConnectionError("API 连接失败")
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return {"status": "success", "data": "result"}
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# ============================================
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# 模式 3：上下文管理器处理资源
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# ============================================
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class DatabaseConnection:
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"""
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自定义上下文管理器，确保资源正确释放
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"""
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def __init__(self, connection_string: str):
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self.connection_string = connection_string
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self.connection = None
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def __enter__(self):
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logger.info(f"连接数据库: {self.connection_string}")
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self.connection = f"Connection to {self.connection_string}"
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return self.connection
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def __exit__(self, exc_type, exc_val, exc_tb):
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if exc_type is not None:
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logger.error(f"发生异常: {exc_val}")
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logger.info("关闭数据库连接")
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# 清理资源
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self.connection = None
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return False # 不抑制异常
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# ============================================
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# 模式 4：链式异常（保留原始异常）
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# ============================================
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def validate_and_process(data: Dict[str, Any]) -> Any:
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"""
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使用 raise from 保留原始异常链
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"""
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try:
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# 验证数据
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if 'value' not in data:
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raise ValueError("数据中缺少 'value' 字段")
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value = data['value']
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if not isinstance(value, (int, float)):
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raise TypeError(f"value 应该是数字，实际类型: {type(value)}")
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# 处理数据
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return value * 2
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except (ValueError, TypeError) as e:
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# 保留原始异常并添加上下文
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raise RuntimeError(f"数据处理失败: {data}") from e
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# ============================================
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# 模式 5：结果对象模式（不使用异常）
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# ============================================
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class Result:
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"""
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结果对象模式：封装成功/失败状态
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"""
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def __init__(self, success: bool, value: Any = None, error: str = None):
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self.success = success
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self.value = value
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self.error = error
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@classmethod
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def ok(cls, value: Any) -> 'Result':
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return cls(success=True, value=value)
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@classmethod
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def err(cls, error: str) -> 'Result':
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return cls(success=False, error=error)
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def is_ok(self) -> bool:
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return self.success
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def is_err(self) -> bool:
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return not self.success
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def unwrap(self) -> Any:
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if not self.success:
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raise ValueError(f"尝试解包错误结果: {self.error}")
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return self.value
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def unwrap_or(self, default: Any) -> Any:
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return self.value if self.success else default
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def safe_divide_result(a: float, b: float) -> Result:
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"""
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使用结果对象而不是异常
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"""
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if b == 0:
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return Result.err(f"除数不能为零: {b}")
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try:
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return Result.ok(a / b)
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except Exception as e:
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return Result.err(f"计算失败: {e}")
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# ============================================
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# 模式 6：多项验证错误收集
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# ============================================
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class ValidationError(Exception):
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"""自定义验证错误"""
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def __init__(self, errors: List[str]):
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self.errors = errors
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super().__init__("\n".join(errors))
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def validate_user(data: Dict[str, Any]) -> None:
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"""
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收集所有验证错误而不是遇到第一个就停止
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"""
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errors = []
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if 'name' not in data:
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errors.append("缺少 'name' 字段")
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elif not isinstance(data['name'], str):
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errors.append("'name' 应该是字符串")
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elif len(data['name']) < 2:
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errors.append("'name' 长度应该至少为 2")
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if 'age' not in data:
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errors.append("缺少 'age' 字段")
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elif not isinstance(data['age'], int):
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errors.append("'age' 应该是整数")
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elif data['age'] < 0 or data['age'] > 150:
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errors.append("'age' 应该在 0-150 之间")
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if 'email' in data and '@' not in data['email']:
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errors.append("'email' 格式不正确")
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if errors:
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raise ValidationError(errors)
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# ============================================
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# 模式 7：默认值和回退
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# ============================================
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def get_config(config: Dict[str, Any], key: str, default: Any = None) -> Any:
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"""
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安全获取配置，支持多级键和默认值
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"""
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if '.' in key:
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# 支持嵌套键，如 "database.host"
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keys = key.split('.')
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value = config
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for k in keys:
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if isinstance(value, dict) and k in value:
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value = value[k]
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else:
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return default
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return value
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# 简单键
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return config.get(key, default)
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# ============================================
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# 模式 8：优雅降级
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# ============================================
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def get_user_preferences(user_id: int) -> Dict[str, Any]:
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"""
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尝试多种方法获取用户偏好，优雅降级
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"""
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# 尝试 1：从缓存获取
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try:
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return _get_from_cache(user_id)
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except Exception as e:
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logger.warning(f"从缓存获取失败: {e}")
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# 尝试 2：从数据库获取
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try:
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return _get_from_database(user_id)
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except Exception as e:
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logger.warning(f"从数据库获取失败: {e}")
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# 尝试 3：使用默认配置
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logger.info("使用默认配置")
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return _get_default_preferences()
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def _get_from_cache(user_id: int) -> Dict[str, Any]:
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# 模拟缓存失败
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raise ConnectionError("缓存连接失败")
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def _get_from_database(user_id: int) -> Dict[str, Any]:
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# 模拟数据库失败
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raise ConnectionError("数据库连接失败")
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def _get_default_preferences() -> Dict[str, Any]:
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return {
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"theme": "light",
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"language": "zh-CN",
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"notifications": True
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}
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# ============================================
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# 测试代码
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# ============================================
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if __name__ == "__main__":
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logging.basicConfig(level=logging.INFO)
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print("=" * 50)
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print("错误处理模式示例")
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print("=" * 50)
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# 测试结果对象模式
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print("\n1. 结果对象模式:")
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result1 = safe_divide_result(10, 2)
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print(f"10 / 2 = {result1.unwrap()}")
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result2 = safe_divide_result(10, 0)
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print(f"10 / 0 = {result2.unwrap_or('N/A')} ({result2.error})")
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# 测试优雅降级
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print("\n2. 优雅降级:")
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prefs = get_user_preferences(123)
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print(f"用户偏好: {prefs}")
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# 测试上下文管理器
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print("\n3. 上下文管理器:")
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try:
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with DatabaseConnection("localhost:5432") as conn:
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print(f"连接: {conn}")
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except Exception as e:
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print(f"操作失败: {e}")
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