Python异常处理之避免try-except滥用的3个核心原则

# 反例：捕获所有异常的模糊处理
def parse_user_data(data):
    try:
        user = json.loads(data)
        age = int(user["age"])
        return {"name": user["name"], "age": age}
    except Exception as e:
        print("解析用户数据失败")
        return None

# 正例：分阶段精准捕获
import json

def parse_user_data(data):
    try:
        user = json.loads(data)
    except json.JSONDecodeError as e:
        print(f"JSON解析失败: {e}, 原始数据: {data[:50]}")
        return None

    try:
        name = user["name"]
        age_str = user.get("age", "18")  # 提供默认值
        age = int(age_str)
    except KeyError as e:
        print(f"缺少必填字段: {e}, 原始数据: {user}")
        return None
    except ValueError as e:
        print(f"age字段类型错误: {e}, 值: {age_str}")
        return None

    return {"name": name, "age": age}

try:
    # 业务代码
except KeyError:  # 最具体的异常
    handle_key_error()
except ValueError:  # 次具体异常
    handle_value_error()
except Exception:  # 最后捕获其他异常
    handle_unexpected_error()

# 反例：过早捕获异常
def calculate_average(numbers):
    try:
        return sum(numbers)/len(numbers)
    except:
        return 0  # 隐藏了空列表、非数字等潜在问题

# 理想开发代码（无try-except）
def divide(a, b):
    return a / b  # 直接暴露ZeroDivisionError

# 生产环境代码
def divide_safe(a, b):
    try:
        return a / b
    except ZeroDivisionError:
        log_error("除数不能为零")
        return float('inf')  # 明确处理策略

# 反例：返回错误码
def query_user(user_id):
    if not isinstance(user_id, int):
        return {"success": False, "msg": "ID必须是整数"}
    # ...业务逻辑

# 正例：抛出异常
def query_user(user_id):
    if not isinstance(user_id, int):
        raise ValueError("用户ID必须是整数类型")
    # ...业务逻辑

# 反例：手动管理文件资源
def read_file_unsafe(path):
    file = None
    try:
        file = open(path)
        return file.read()
    except IOError:
        print("文件读取失败")
        return None
    finally:
        if file:  # 存在未关闭文件的风险
            file.close()

# 正例：使用上下文管理器
def read_file_safe(path):
    try:
        with open(path) as file:
            return file.read()
    except FileNotFoundError:
        print(f"文件不存在: {path}")
        return None
    except PermissionError:
        print(f"无权限访问: {path}")
        return None

import sqlite3
from contextlib import contextmanager

@contextmanager
def db_connection(db_path):
    conn = None
    try:
        conn = sqlite3.connect(db_path)
        yield conn
    except sqlite3.Error as e:
        print(f"数据库错误: {e}")
        raise  # 重新抛出异常
    finally:
        if conn:
            conn.close()

# 使用示例
with db_connection("test.db") as conn:
    cursor = conn.cursor()
    cursor.execute("SELECT * FROM users")
    # ...业务逻辑

import logging

logging.basicConfig(
    filename='app.log',
    level=logging.ERROR,
    format='%(asctime)s - %(levelname)s - %(message)s'
)

def divide(a, b):
    try:
        return a / b
    except ZeroDivisionError:
        logging.error("除零错误发生", exc_info=True)  # 记录完整堆栈
        raise

# 低效写法（循环中频繁异常）
def find_index(items, target):
    for i, item in enumerate(items):
        try:
            if item == target:
                return i
        except TypeError:
            continue
    return -1

# 高效写法（先检查类型）
def find_index_optimized(items, target):
    if not isinstance(target, (int, float, str)):  # 提前检查
        return -1
    for i, item in enumerate(items):
        if item == target:
            return i
    return -1