异常处理.ipynb · BlackSheep/python精进

加入 Gitee

与超过 1200万开发者一起发现、参与优秀开源项目，私有仓库也完全免费：）

该仓库未声明开源许可证文件（LICENSE），使用请关注具体项目描述及其代码上游依赖。

克隆/下载

异常处理.ipynb 10.94 KB

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Python的异常处理机制主要依赖try、except、else、finally和raise五个关键字  \n",
    "\n",
    "* try代码块中放置的是可能引发异常的代码\n",
    "* 在except关键字后对应的是异常类型和一个代码块, 用于表明该except块处理这种类型的异常\n",
    "* else代码块中放置程序未出现异常后要继续执行的代码\n",
    "* finally代码块用于回收在try块中打开的物理资源, 异常机制会保证finally块总被执行\n",
    "* raise用于自行引发异常"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "重点讲一下try和except"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "```python\n",
    "try:\n",
    "    可能出错的代码\n",
    "except Error as e:\n",
    "    异常处理代码\n",
    "```"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 1.1 异常处理机制"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**原理**"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "如果try代码块中的代码出现异常, 系统自动生成一个异常对象, 该异常对象被提交给Python解释器, 这个过程被称为**引发异常**  \n",
    "\n",
    "当Python解释器收到异常对象时, 会寻找能处理该异常对象的except块(*如果有多个except块, 会依次判断该异常对象是否是except块后的异常类或其子类的实例*), 如果找到合适的except块, 则把该异常对象交给该except块处理, 这个过程被称为**捕获异常**. 如果Python解释器找不到捕获异常的except块, 则运行时环境终止, Python解释器也将退出.  \n",
    "\n",
    "但不管出错的代码是位于try代码块中, 还是except块中, 还是其他地方, 只要代码出现了异常, 系统总会自动生成一个Error对象. 如果程序没有为出错的代码定义任何的except块, 则Python解释器无法找到处理该异常的except块, 程序就在此退出."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**Python异常捕获流程**"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "![](../../jupyter_notebook图片/Python异常捕获流程示意图.png)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**异常类之间的继承关系**"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "![](../../jupyter_notebook图片/Python异常类之间的继承关系.png)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "BaseException的主要子类就是Exception, 不管是系统的异常类, 还是用户自定义的异常类, 都应该从Exception派生"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "最后, 处理异常时要将所有父类异常的except块排在子类异常的except块的后面(即: 应先处理小异常, 再处理大异常)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    " "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    " "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    " "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 1.2 不同类型的try、except"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "一个异常类, 一种处理"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "```python\n",
    "import sys\n",
    "\n",
    "try:\n",
    "    a = int(sys.argv[1])\n",
    "    b = int(sys.argv[2])\n",
    "    c = a / b\n",
    "    print('你输入的两个数相除的结果是:', c)\n",
    "except IndexError:\n",
    "    print('索引错误: 运行程序时输入的参数个数不够')\n",
    "    ```"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "多个异常类, 多种处理"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "```python\n",
    "import sys\n",
    "\n",
    "try:\n",
    "    a = int(sys.argv[1])\n",
    "    b = int(sys.argv[2])\n",
    "    c = a / b\n",
    "    print('你输入的两个数相除的结果是:', c)\n",
    "except IndexError:\n",
    "    print('索引错误: 运行程序时输入的参数个数不够')\n",
    "except ValueError:\n",
    "    print('数值错误: 程序只能接受整数参数')\n",
    "except ArithmeticError:\n",
    "    print('算数错误')\n",
    "except Exception:  # 处理异常时要将所有父类异常的except块排在子类异常的except块的后面\n",
    "    print('未知异常')\n",
    "```"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    " "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "```python\n",
    "import sys\n",
    "\n",
    "try:\n",
    "    a = int(sys.argv[1])\n",
    "    b = int(sys.argv[2])\n",
    "    c = a / b\n",
    "    print('你输入的两个数相除的结果是:', c)\n",
    "except (IndexError, ValueError, ArthmeticError): # 在使用一个except块捕获多种类型的异常时, 只要将多个异常类用圆括号括起来, 中间用逗号隔开即可 --- 其实就是构建多个异常类的元组\n",
    "    print('程序发生了数组越界、数字格式异常、算术异常之一')\n",
    "except: # 只有except关键字, 表示可捕获所有类型的异常, 一般会作为异常捕获的最后一个except块\n",
    "    print('未知异常')\n",
    "    ```"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "多个异常类, 一种处理"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "```python\n",
    "import sys\n",
    "\n",
    "try:\n",
    "    a = int(sys.argv[1])\n",
    "    b = int(sys.argv[2])\n",
    "    c = a / b\n",
    "    print('你输入的两个数相除的结果是:', c)\n",
    "except Exception:\n",
    "    print('未知异常')\n",
    "    ```"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    " "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "```python\n",
    "import sys\n",
    "\n",
    "try:\n",
    "    a = int(sys.argv[1])\n",
    "    b = int(sys.argv[2])\n",
    "    c = a / b\n",
    "    print('你输入的两个数相除的结果是:', c)\n",
    "except: # 只有except关键字, 表示可捕获所有类型的异常, 一般会作为异常捕获的最后一个except块\n",
    "    print('未知异常')\n",
    "    ```"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    " "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "```python\n",
    "import sys\n",
    "\n",
    "try:\n",
    "    a = int(sys.argv[1])\n",
    "    b = int(sys.argv[2])\n",
    "    c = a / b\n",
    "    print('你输入的两个数相除的结果是:', c)\n",
    "except (IndexError, ValueError, ArthmeticError):\n",
    "    print('程序发生了数组越界、数字格式异常、算术异常之一')\n",
    "    ```"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 1.3 访问异常信息"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "访问异常信息"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {},
   "outputs": [],
   "source": [
    "def foo():\n",
    "    try:\n",
    "        fis = open('a.txt')\n",
    "    except Exception as e: # 只要在单个异常类或异常类元组(多异常捕获)之后加上as再加上异常变量即可获取异常对象的相关信息\n",
    "        print(e.args) # args: 该属性返回异常的错误编号和描述字符串\n",
    "        print(e.errno) # errno: 该属性返回异常的错误编号\n",
    "        print(e.strerror) # strerror: 该属性返回异常的描述字符串"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "scrolled": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "(2, 'No such file or directory')\n",
      "2\n",
      "No such file or directory\n"
     ]
    }
   ],
   "source": [
    "foo()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {},
   "outputs": [],
   "source": [
    "def foo2():\n",
    "    try:\n",
    "        fis = open('a.txt')\n",
    "    except (FileNotFoundError, IndexError) as e:\n",
    "        print(e.args)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {
    "scrolled": true
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "(2, 'No such file or directory')\n"
     ]
    }
   ],
   "source": [
    "foo2()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "  "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    " "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    " "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    " "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    " "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "在Python的异常处理流程中还可以添加一个else块, 当try块没有出现异常时, 程序会执行else块"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "举例来说"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "```python\n",
    "s = input('请输入整数')\n",
    "try:\n",
    "    result = 20 / int(s)\n",
    "except ValueError:\n",
    "    print('值错误, 必须输入数值')\n",
    "except ArithmeticError:\n",
    "    print('算数错误, 不能输入0')\n",
    "else:\n",
    "    print('没有出现异常')\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
 ],
 "metadata": {
  "kernelspec": {
   "display_name": "Python 3",
   "language": "python",
   "name": "python3"
  },
  "language_info": {
   "codemirror_mode": {
    "name": "ipython",
    "version": 3
   },
   "file_extension": ".py",
   "mimetype": "text/x-python",
   "name": "python",
   "nbconvert_exporter": "python",
   "pygments_lexer": "ipython3",
   "version": "3.7.3"
  },
  "toc": {
   "base_numbering": 1,
   "nav_menu": {},
   "number_sections": false,
   "sideBar": true,
   "skip_h1_title": false,
   "title_cell": "Table of Contents",
   "title_sidebar": "Contents",
   "toc_cell": false,
   "toc_position": {
    "height": "calc(100% - 180px)",
    "left": "10px",
    "top": "150px",
    "width": "512px"
   },
   "toc_section_display": true,
   "toc_window_display": true
  }
 },
 "nbformat": 4,
 "nbformat_minor": 2
}

一键复制编辑原始数据按行查看历史

提交于 2020-02-14 00:24 . 异常处理

Python

https://gitee.com/blackSheepWall0305/python_refinement.git

git@gitee.com:blackSheepWall0305/python_refinement.git

blackSheepWall0305

python_refinement

python精进

master

BlackSheep / python精进

简介

发行版

贡献者

近期动态

BlackSheep / python精进 .gitee-modal { width: 500px !important; }

简介

发行版

贡献者

近期动态

搜索帮助

BlackSheep / python精进