Python异常处理操作举例详细教程

try:
    # 可能引发异常的代码
    result = 10 / 0
except ZeroDivisionError:
    # 处理特定异常
    print("不能除以零!")
except Exception as e:
    # 通用异常处理
    print(f"发生错误: {e}")
else:
    # 无异常时执行
    print("计算成功")
finally:
    # 始终执行的清理代码
    print("清理资源")

BaseException
 ├── KeyboardInterrupt
 ├── SystemExit
 └── Exception
      ├── ArithmeticError
      │    ├── ZeroDivisionError
      │    └── FloatingPointError
      ├── LookupError
      │    ├── IndexError
      │    └── KeyError
      ├── OSError
      │    ├── FileNotFoundError
      │    └── PermissionError
      └── ValueError

# 文件操作
try:
    with open("nonexist.txt") as f:
        content = f.read()
except FileNotFoundError:
    print("文件不存在")

# 类型转换
try:
    num = int("abc")
except ValueError:
    print("无效的数字格式")

# 字典操作
d = {"key": "value"}
try:
    print(d["missing"])
except KeyError:
    print("键不存在")

try:
    # 可能抛出多种异常的代码
except (TypeError, ValueError) as e:
    print(f"输入类型错误: {e}")

try:
    data = json.loads(invalid_json)
except json.JSONDecodeError:
    print("JSON解析失败")
except Exception:
    print("其他未知错误")

file = None
try:
    file = open("data.txt", "r")
    process(file)
except IOError:
    print("文件操作错误")
finally:
    if file:
        file.close()  # 确保资源释放

try:
    result = risky_operation()
except NetworkError:
    handle_error()
else:
    save_result(result)  # 仅在成功时执行

class InvalidEmailError(ValueError):
    """自定义邮箱格式异常"""
    def __init__(self, email):
        super().__init__(f"无效邮箱格式: {email}")
        self.email = email

# 使用示例
email = "user@"
if "@" not in email or "." not in email.split("@")[1]:
    raise InvalidEmailError(email)

class DatabaseError(Exception):
    """数据库操作基类异常"""

class ConnectionError(DatabaseError):
    """数据库连接异常"""

class QueryError(DatabaseError):
    """SQL查询异常"""

try:
    config = load_config()
except FileNotFoundError as e:
    raise RuntimeError("配置加载失败") from e

try:
    # 可能出错的代码
except Exception as e:
    print("原始异常:", e.__cause__)
    print("上下文:", e.__context__)

raise ValueError(f"无效参数值: {value}")

import logging
try:
    process()
except Exception:
    logging.exception("处理失败")

try:
    ...
except:  # 捕获所有异常，包括KeyboardInterrupt
    pass

try:
    ...
except Exception:
    pass  # 静默失败

try:
    ...
except Exception as e:
    print(e)
    raise  # 保留原始堆栈信息

import requests
from time import sleep

def fetch_data(url, retries=3):
    for attempt in range(retries):
        try:
            response = requests.get(url, timeout=5)
            response.raise_for_status()
            return response.json()
        except requests.HTTPError as e:
            print(f"HTTP错误: {e}")
        except requests.Timeout:
            print("请求超时")
        except requests.RequestException:
            print("网络连接问题")
        
        if attempt < retries - 1:
            sleep(2 ** attempt)  # 指数退避
    raise Exception(f"请求失败，已重试{retries}次")

# 使用示例
data = fetch_data("https://api.example.com/data")