{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "# [X-Village] Lesson 05 - Exception Basics\n",
    "\n",
    "by 洪培軒"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## Outline\n",
    "\n",
    "* 看懂 error message\n",
    "* 了解什麼是 exception\n",
    "* 為什麼需要 Exception Handling\n",
    "* 基本的語法\n",
    "* 自定義 exception\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "# <center>如何看懂 error message</center>\n",
    "\n",
    "<center><img src=\"index_error_2.png\"/></center>"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## 1. scope -- `in xxx`\n",
    "\n",
    "告訴你那些問題在哪個 scope 被發現的"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "source": [
    "<img src=\"err_scope.png\" />"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## 2. Traceback\n",
    "告訴你程式經歷了哪些大風大浪才死去"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [],
   "source": [
    "# traceback.py\n",
    "def take(key):\n",
    "  print(dic[key])\n",
    "\n",
    "def generate_key(code):\n",
    "  key = str(code)+'A'\n",
    "  take(key)\n",
    "\n",
    "def generate_code(data):\n",
    "  code = data%4\n",
    "  generate_key(code)\n",
    "\n",
    "def walk_in(data):\n",
    "  generate_code(data)\n",
    "\n",
    "dic = {'0A': 'plate', '1A': 'spoon'}\n",
    "walk_in(11)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "<img src=\"code_traceback.png\"/>\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "<img src=\"code_traceback_pic.png\">"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## 3. exception 的名字 -- `IndexError`\n",
    "錯誤的『名稱』，還有錯誤的『說明』"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "scrolled": true,
    "slideshow": {
     "slide_type": "-"
    }
   },
   "outputs": [],
   "source": [
    "# wrong.py\n",
    "a = [123, 345, 789]\n",
    "print(a[3]) # line 2"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "source": [
    "<img src=\"err_name.png\">"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## 練習 1  (ex1)\n",
    "\n",
    "下面程式碼希望能夠印出 num 裏面的所有數字，但是程式跑到一半會出錯。\n",
    "\n",
    "執行後解釋出現的錯誤訊息，並說出程式在哪裡出了問題。\n",
    "\n",
    "TIPS: 如果不知道出現的 exception 代表什麼意思，可以參考 [python 內建的 exception](https://docs.python.org/3.6/library/exceptions.html)\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [],
   "source": [
    "def div(dividend, divisor):\n",
    "    print(\"The answer is {}\".format(dividend/divisor))\n",
    "\n",
    "for i in range(5, -1, -1):\n",
    "    for j in range(5, -1, -1):\n",
    "        div(i, j)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "source": [
    "\n",
    "## 練習 2 (ex2.py)\n",
    "\n",
    "更改上面程式碼讓程式可以正常運作"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "# <center>exception 是什麼</center>\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## <center>exception 就是炸彈</center>\n",
    "\n",
    "* try\n",
    "* except\n",
    "* finally\n",
    "* raise\n",
    "\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "\n",
    "1. 做好會隨時拿到炸彈的『準備』\n",
    "2. 『拿到炸彈』就自己『拆掉』，不然就『丟給別人』拆\n",
    "3. 丟炸彈要看時機（想『炸敵人』還是『炸同伴』）"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "* 隊友太雷就炸隊友 -> 提醒隊友不要粗心\n",
    "* 敵人太強也炸敵人 -> 讓 bug 比較容易被發現\n",
    "------------\n",
    "* 做準備 -> try\n",
    "* 拆炸彈 -> except\n",
    "* 丟炸彈 -> raise\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## <center>有不同的 exception</center>\n",
    "<center>就像炸彈也有不同的種類</center>\n",
    "\n",
    "* 地雷\n",
    "* 手榴彈\n",
    "* 原子彈\n",
    "* ...."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## <center>常見的 exception</center>\n",
    "* ValueError\n",
    "* NameError\n",
    "* SyntaxError\n",
    "* IndentationError"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "* ValueError: 正確的型態，不正確的值"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [],
   "source": [
    "print(int(\"a\"))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [],
   "source": [
    "print(int(\"1\"))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "* NameError: 使用到沒有定義過的 name"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [],
   "source": [
    "ggg_abc()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "outputs": [],
   "source": [
    "\n",
    "def ggg_abc():\n",
    "    print(\"in ggg_abc()\")\n",
    "gggg_abc()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "* SyntaxError: 語法錯誤\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [],
   "source": [
    "print('hello world\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "source": [
    "EOL: End of Line"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [],
   "source": [
    "print('hello world!')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "* IndentationError: 縮排錯誤"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "outputs": [],
   "source": [
    "if True:\n",
    "print(\"ok!\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "outputs": [],
   "source": [
    "if True:\n",
    "    print(\"ok!\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "\n",
    "<img src=\"hierarchy.png\"></img>"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "# <center>為什麼我們需要 Exception Handling</center>\n",
    "\n",
    "## 用途\n",
    "1. 易讀性，減少累贅的判斷式\n",
    "\n",
    "2. 避免使用回傳值作為判斷依據（有時候會忘記）\n",
    "\n",
    "3. 預期中會產生的錯誤，但是不希望程式中止\n",
    "\n",
    "    \n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "<img src=\"give_example.jpg\" />\n",
    "[圖片取自網路](https://www.fabiaoqing.com/biaoqing/detail/id/53371.html)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## 小明買醬油的故事"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "source": [
    "1. 直接回家跟媽媽講沒醬油了 -> 沒有買東西 -> 晚餐沒有味道"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "source": [
    "2. 打電話回家，不買到東西不離開 -> 可以買鹽來代替 -> 晚餐有味道"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## 用宿網打 game"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "source": [
    "<img src=\"https://gss0.baidu.com/-4o3dSag_xI4khGko9WTAnF6hhy/zhidao/pic/item/7dd98d1001e939011d2b8d2370ec54e736d19685.jpg\" />\n",
    "\n",
    "[圖片來源](https://zhidao.baidu.com/question/629629479260473044.html)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "notes"
    }
   },
   "source": [
    "## 小明買醬油的故事\n",
    "\n",
    "媽媽叫小明去買醬油。\n",
    "\n",
    "小明去了超市後發現沒有醬油，就直接回家了。\n",
    "\n",
    "晚餐時間大家在吃飯發現飯菜都沒有味道。\n",
    "\n",
    "---------------------\n",
    "\n",
    "如果我們有 exception 呢？\n",
    "\n",
    "小明會在超市打電話問媽媽說沒醬油了，媽媽讓他買其他東西來代替醬油。\n",
    "\n",
    "如果沒有買到醬油的替代品，小明就不會離開超市。\n",
    "\n",
    "---------------------\n",
    "\n",
    "差別：\n",
    "\n",
    "沒有 exception 的話，晚餐可能不會是我們想要的 --> 程式可以執行，但是有 bug而且不知道在哪裡發生的\n",
    "\n",
    "有 exception 的話，小明會**提醒**媽媽沒有醬油，是不是要買其他東西 --> 程式有問題，在解決之前沒辦法執行（或是執行到一半會死掉）"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "notes"
    }
   },
   "source": [
    "## 用宿網打 game\n",
    "\n",
    "開開心心打遊戲，大家在會戰的突然掉線了。\n",
    "\n",
    "原來是宿網斷線了啊！但是遊戲程式有因為網路斷線而出現錯誤嗎？\n",
    "\n",
    "沒有！頂多告訴你你已經斷線了，請嘗試重新連線。\n",
    "\n",
    "為什麼程式不會中斷？因為我們用 exception 把他抓住了，並且在後面寫下如果遇到網路斷線時應該要做什麼。\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "# <center>遇到 Exception 之後...</center>\n",
    "\n",
    "* try....except...else\n",
    "* try....except as e\n",
    "* finally\n",
    "* raise"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## try...except...[else]\n",
    "最基本的語法"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "outputs": [],
   "source": [
    "try:\n",
    "    # do something\n",
    "except Exception:\n",
    "    # handle the exception\n",
    "else:\n",
    "    # optional, if no exception happens"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "scrolled": true,
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [],
   "source": [
    "try:\n",
    "    print(\"In try block\")\n",
    "except Exception:\n",
    "    print(\"In Exception block\")\n",
    "else:\n",
    "    print(\"No exception\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## 練習（不計分）\n",
    "\n",
    "寫出一個會產生 exception 的程式，並用 try...except...else 接起來"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## try...except...as e\n",
    "e 會是抓到的那個 exception 的 instance object\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "outputs": [],
   "source": [
    "# run me!\n",
    "try:\n",
    "    num = x\n",
    "except NameError as e:\n",
    "    print(e)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## 練習（不計分）\n",
    "\n",
    "* 試著用 `type(e)` 看 e 是什麼型別的\n",
    "* 試著用 `instance.args` 看看這個 object 的 attribute 有哪些\n",
    "* 試著產生其他的 exception 再把他印出來看看\n",
    "\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## 多個 exception"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "outputs": [],
   "source": [
    "# run me!\n",
    "a = [1, 2, 3]\n",
    "try:\n",
    "    print(a[100])\n",
    "    num = x\n",
    "except NameError as e:\n",
    "    print(\"I'm in NameError! \")\n",
    "    print(e)\n",
    "except IndexError as e:\n",
    "    print(\"I'm in IndexError!\" )\n",
    "    print(e)\n",
    "else:\n",
    "    print(\"I'm in else!\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "### 另一種寫法\n",
    "(把 print(a[100]) 和 num = x 互換看看)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "outputs": [],
   "source": [
    "# run me!\n",
    "a = [1,2,3]\n",
    "try:\n",
    "    print(a[100])\n",
    "    num = x\n",
    "except (NameError, IndexError) as e:\n",
    "    print(e)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## finally\n",
    "不論是否產生 exception, 『最後』一定會被執行到的區塊"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "outputs": [],
   "source": [
    "try:\n",
    "    print(\"hello!\")\n",
    "    x = gggggg\n",
    "except Exception as e:\n",
    "    print(e)\n",
    "else:\n",
    "    print(\"In else\")\n",
    "\n",
    "print(\"I'm in finally!\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "### 練習（不計分）\n",
    "如果把 finally 刪掉會怎樣呢？"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "### 為什麼需要 finally?\n",
    "\n",
    "比較這兩種程式碼："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [],
   "source": [
    "def func():\n",
    "    try:\n",
    "        print(\"hello\")\n",
    "    except Exception:\n",
    "        print(\"in exception\")\n",
    "        return\n",
    "    # do something\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "outputs": [],
   "source": [
    "def func():\n",
    "    try:\n",
    "        print(\"hello\")\n",
    "    except Exception:\n",
    "        print(\"in exception\")\n",
    "        return\n",
    "    finally:\n",
    "        # do something"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "### 實際上來操作一次"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [],
   "source": [
    "# run me!\n",
    "def func():\n",
    "    try:\n",
    "        print(\"I'm in try block!\")\n",
    "        a = bggggggg\n",
    "    except Exception:\n",
    "        print(\"I'm in except block!\")\n",
    "        return\n",
    "    finally:\n",
    "        print(\"do something\")\n",
    "        \n",
    "func()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "source": [
    "### 練習（不計分）\n",
    "把 finally 去掉再試試看，會發生什麼事？"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## raise\n",
    "丟出一個 exception 給別人接"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [],
   "source": [
    "# run me!\n",
    "def div(a, b):\n",
    "    if b == 0:\n",
    "        raise ValueError(\"divisor cannot be zero!\")\n",
    "    else: return a/b\n",
    "\n",
    "num = div(1,0)\n",
    "print(num)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## 練習 3 (ex3.py)\n",
    "\n",
    "寫一個 function，function 需要 raise exception\n",
    "\n",
    "呼叫 function 的時候需要用 try...except 包起來\n",
    "    \n",
    "**挑戰題 1 (ex5.py)**\n",
    "\n",
    "實做 **小明買醬油** 的故事"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## 挑戰題的範例（把 TODO 解掉）"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "outputs": [],
   "source": [
    "import random\n",
    "item_in_shop = {\"soybean_sauce\": 0, \"milk\": 4, \"salt\": 10, \"soybean_milk\": 3}\n",
    "items = [item for item in item_in_shop.keys()]\n",
    "cnt = 5\n",
    "\n",
    "def buy(item):\n",
    "    # TODO: 補上程式碼和完成邏輯\n",
    "    # tips: 如果東西數量是 0 需要 raise Exception,否則就把物品的數量減 1 \n",
    "    print(\"Mommy! I've bought {} for you!\".format(item))\n",
    "\n",
    "# 買五個隨機的東西\n",
    "while cnt:\n",
    "    cnt -= 1\n",
    "    index = random.randint(0,3)\n",
    "    item = items[index]\n",
    "    \n",
    "    # 想要買的東西是 item，利用 buy() 來買東西\n",
    "    # TODO: 補上程式碼\n",
    "    # tips: 記得用 try...except 包起來\n",
    " "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## <center>為什麼我們需要 Exception Handling</center>"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "source": [
    "<center>以 python 的語法來實際比較看看</center>"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "1. 易讀性，減少累贅的判斷式\n",
    "\n",
    "    **沒有使用 exception 的時候**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [],
   "source": [
    "def calc_percentage(dividend, divisor):\n",
    "    if divisor == 0:\n",
    "        return -1\n",
    "    else:\n",
    "        return 100.0*dividend/divisor\n",
    "\n",
    "a1 = calc_percentage(25.0, 100.0)    \n",
    "a2 = calc_percentage(30.0, 56.0)    \n",
    "a3 = calc_percentage(16.0, 49.0)\n",
    "\n",
    "if a1 == -1:\n",
    "    print(\"Not vaild divisor\")\n",
    "else:\n",
    "    print(\"The answer is \" + str(a1)+\"%\")\n",
    "\n",
    "if a2 == -1:\n",
    "    print(\"Not vaild divisor\")\n",
    "else:\n",
    "    print(\"The answer is \" + str(a2)+\"%\")\n",
    "\n",
    "if a3 == -1:\n",
    "    print(\"Not vaild divisor\")\n",
    "else:\n",
    "    print(\"The answer is \" + str(a3)+\"%\")\n",
    "    "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "1. 易讀性，減少累贅的判斷式\n",
    "\n",
    "    **使用 exception 的時候**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [],
   "source": [
    "def calc_percentage(dividend, divisor):\n",
    "    if divisor == 0:\n",
    "        raise ZeroDivisionError(\"Divisor cannot be zero!\")\n",
    "    else:\n",
    "        return 100.0*dividend/divisor\n",
    "\n",
    "a1 = calc_percentage(25.0, 100.0)\n",
    "a2 = calc_percentage(30.0, 56.0)\n",
    "a3 = calc_percentage(16.0, 49.0)\n",
    "print(\"The answer is \" + str(a1)+\"%\")\n",
    "print(\"The answer is \" + str(a2)+\"%\")\n",
    "print(\"The answer is \" + str(a3)+\"%\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "2. 避免使用回傳值作為判斷的依據（有時候會忘記，尤其是如果 function 不是自己寫的時候）\n",
    "\n",
    "    **沒有使用 exception 的時候**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "outputs": [],
   "source": [
    "def calc_percentage(dividend, divisor):\n",
    "    if divisor == 0:\n",
    "        return -1\n",
    "    else:\n",
    "        return 100.0*dividend/divisor\n",
    "\n",
    "answer = calc_percentage(25.0, 0.0)\n",
    "print(\"The answer is \" + str(answer)+\"%\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "2. 避免使用回傳值作為判斷的依據（有時候會忘記，尤其是如果 function 不是自己寫的時候）\n",
    "\n",
    "    **使用 exception 的時候**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "outputs": [],
   "source": [
    "def calc_percentage(dividend, divisor):\n",
    "    if divisor == 0:\n",
    "        raise ZeroDivisionError(\"Divisor cannot be zero!\")\n",
    "    else:\n",
    "        return 100.0*dividend/divisor\n",
    "\n",
    "answer = calc_percentage(25.0, 0.0)\n",
    "print(\"The answer is \" + str(answer)+\"%\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## 練習 (不計分）\n",
    "\n",
    "使用已經寫好的 function，**隨機**取出 list 裏面的資料，請找出程式的問題。\n",
    "\n",
    "TIPS：多執行幾次看看\n",
    "\n",
    "註： get_index_random(m, n) 可以得到一個隨機的 index，可以多執行幾次看看問題出在那邊"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [],
   "source": [
    "import random\n",
    "def get_index_random(m, n):\n",
    "    # Does not expect m to be 1, return -1\n",
    "    if m==1:\n",
    "        return -1\n",
    "    return (n+m+random.randint(0,4))%4\n",
    "\n",
    "my_list = ['apple', 'banana', 'cherry', 'dog']\n",
    "\n",
    "for i in range(10):\n",
    "    for j in range(10):\n",
    "        index = get_index_random(i, j)\n",
    "        print(my_list[index])"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## 解答"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "scrolled": false,
    "slideshow": {
     "slide_type": "-"
    }
   },
   "outputs": [],
   "source": [
    "import random\n",
    "def get_index_random(m, n):\n",
    "    # Does not expect m to be 1, return error code\n",
    "    if m==1:\n",
    "        return -1\n",
    "    return (n+m+random.randint(0,4))%4\n",
    "\n",
    "my_list = ['apple', 'banana', 'cherry', 'dog']\n",
    "\n",
    "for i in range(10):\n",
    "    for j in range(10):\n",
    "        index = get_index_random(i, j)\n",
    "        # ------加上判斷式------\n",
    "        if index==-1:\n",
    "            print(\"m cannot be 1, try another m value\");\n",
    "        # -------------------\n",
    "        else: print(my_list[index])"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "# <center>自定義 exception</center>\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## <center>為什麼我們需要自己定義 exception?</center>"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## <center>如何自己定義 exception</center>\n",
    "\n",
    "定義一個新的 class\n",
    "* 繼承 Exception\n",
    "* 定義一些 special method\n",
    "    1. `__init__(self[,...])`\n",
    "        用來初始化\n",
    "    2. `__str__(self)`\n",
    "        用來印出內容\n",
    "        \n",
    "    [延伸閱讀](https://docs.python.org/3/reference/datamodel.html#special-method-names)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "### 做一次看看吧！"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "outputs": [],
   "source": [
    "# run me!\n",
    "class MyException(Exception):\n",
    "    def __init__(self, err_msg):\n",
    "        self.msg = err_msg\n",
    "    def __str__(self):\n",
    "        return \"abc\" + self.msg\n",
    "\n",
    "try:\n",
    "    raise MyException(\"I'm an exception message!\")\n",
    "except MyException as e:\n",
    "    print(\"---encountered MyEception---\")\n",
    "    print(e)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## 練習 4 (ex4.py)\n",
    "\n",
    "自己定義一個 exception 叫作 RelationException\n",
    "\n",
    "在 raise 的時候需要能夠接受 2 個字串，像是這樣 `raise RelationException(\"Mommy\", \"Daddy\")`\n",
    "\n",
    "輸出的時候需要以下列格式印出 (P1 和 P2 是 raise exception 時傳入的參數)\n",
    "\n",
    "`Are you sure that P1 and P2 are in love with each other?`"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## 補齊程式碼 （把有 TODO 的地方都改掉）"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "outputs": [],
   "source": [
    "'''\n",
    "TODO: define a exception class\n",
    "'''\n",
    "relation = {'Jason':'Mary', 'Mary':'Jason', 'Jennifer':'Ken', 'Ken':'Jennifer', 'Tina':'Kim', 'Kim':'Tina'}\n",
    "def check(pa, pb):\n",
    "    if relation[pa] != pb:\n",
    "        # TODO: raise exception\n",
    "        # TIPS: 這個地方會需要 raise 兩種 exception\n",
    "    \n",
    "try:\n",
    "    p1 = input(\"Please enter the first person: \")\n",
    "    p2 = input(\"Please enter the second person: \")\n",
    "    check(p1, p2)\n",
    "    print(\"{} and {} are in love with each other!\".format(p1, p2))\n",
    "    \n",
    "except '''what exception?''' as e:\n",
    "    print(e)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## 測資\n",
    "\n",
    "輸入：\n",
    "\n",
    "    Jason\n",
    "    \n",
    "    Mary\n",
    "    \n",
    "輸出：\n",
    "\n",
    "    Jason and Mary are in love with each other!\n",
    "    \n",
    "-----\n",
    "輸入：\n",
    "\n",
    "    Jen\n",
    "    \n",
    "    Ducky\n",
    "    \n",
    "輸出：\n",
    "\n",
    "    No relation found\n",
    "    Are you sure that Jen and Ducky are in love with each other?\n",
    "    \n",
    "-----\n",
    "輸入：\n",
    "\n",
    "    Jason\n",
    "    \n",
    "    Jennifer\n",
    "    \n",
    "輸出：\n",
    "\n",
    "    Are you sure that Jason and Jennifer are in love with each other?\n",
    "    \n",
    "-----"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## 挑戰題2 (ex6.py)\n",
    "\n",
    "### 解釋\n",
    "\n",
    "* 三個數值：飢餓度，口渴度，開心度\n",
    "\n",
    "* 有三個動作，分別會消耗一些數值\n",
    "    * play\n",
    "    * eat\n",
    "    * drink   "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "    \n",
    "* 需要三個 exception，分別是 \n",
    "    * HungryException\n",
    "    * ThirstyException\n",
    "    * BoredException"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "### 目標\n",
    "1. 定義出這三種不同的 exception\n",
    "2. 決定哪時候應該要 raise 哪個 exception\n",
    "3. 決定遇到 exception 時的處理方式，並且印出字串\n",
    "    * `I'm _____ (status: xxx), need to ......`\n",
    "    * `___`和`xxx`和`...`因為不同狀況會是不同字串"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## 補齊程式碼"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "outputs": [],
   "source": [
    "import random\n",
    "\n",
    "'''\n",
    "TODO: define exception classes\n",
    "'''\n",
    "\n",
    "def check(man):\n",
    "    # TODO: in what condition need to raise exception?\n",
    "    \n",
    "def play(man):\n",
    "    print(\"playing...\")\n",
    "    man[\"hunger\"] -= 15\n",
    "    man[\"water\"] -= 15\n",
    "    man[\"mood\"] += 5\n",
    "    check(man)\n",
    "def eat(man):\n",
    "    print(\"eating...\")\n",
    "    man[\"hunger\"] += 5\n",
    "    check(man)\n",
    "def drink(man):\n",
    "    print(\"drinking...\")\n",
    "    man[\"water\"] += 5\n",
    "    check(man)\n",
    "    \n",
    "actionList = [play, eat, drink]\n",
    "    \n",
    "child = {\"hunger\": 20, \"water\": 20, \"mood\": 20}\n",
    "\n",
    "while True:\n",
    "    cnt -= 1\n",
    "    rand = random.randint(0,2)\n",
    "    \n",
    "    # TODO: 把隨機的動作用 try...except 包起來   \n",
    "    actionList[rand](child)\n",
    "    # TIPS: 記得只要抓到 exception 之後就要 break 了，不然會造成無窮迴圈 "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "### 可能會出現的結果"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "-"
    }
   },
   "source": [
    "playing...\n",
    "\n",
    "drinking...\n",
    "\n",
    "drinking...\n",
    "\n",
    "drinking...\n",
    "\n",
    "playing...\n",
    "\n",
    "I'm hungry (status: -10), need to eat!\n",
    "\n",
    "eating..."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## 挑戰題 (ex7.py)\n",
    "\n",
    "參考墜樓的故事，把故事敘述用程式碼表達\n",
    "   "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "小明在 106 樓看風景，不小心腳一滑從 106 樓掉下去。\n",
    "\n",
    "這時候會觸發大樓的安全機關（FallDownException)，但是因為小明太胖了所以第一層安全機關會被突破。\n",
    "\n",
    "好險大樓還有第二層安全機關（FallDownStrongerException)，最後終於把小明接住了！\n",
    "\n",
    "\n"
   ]
  },
  {
   "cell_type": "markdown",
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     "slide_type": "subslide"
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   "source": [
    "定義兩個 exception，分別是\n",
    "* FallDownException(Exception)\n",
    "* FallDownStrongerException(Exception)\n",
    "\n",
    "定義一個函式\n",
    "* slip(floor)\n",
    "    * 小明必須要在第 80 樓觸發 FallDownException, 在第 5 樓觸發 FallDownStrongerException\n",
    "    * 觸發時記得要印出： 在 xx 樓被接住了！"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "### 輸出\n",
    "\n",
    "現在在 105 樓\n",
    "\n",
    "現在在 104 樓\n",
    "\n",
    "....（略）\n",
    "\n",
    "在 80 樓被接住了！\n",
    "\n",
    "突破機關！\n",
    "\n",
    "....（略）\n",
    "\n",
    "現在在 5 樓\n",
    "\n",
    "在 5 樓被接住了！\n",
    "\n",
    "安全！\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "## 補齊程式碼"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
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   "source": [
    "# TODO: 按照敘述定義出兩個 Exception\n",
    "    \n",
    "def slip(floor):\n",
    "    try:\n",
    "        while floor:\n",
    "            floor -= 1\n",
    "            print(\"現在在 {} 樓\".format(floor))\n",
    "\n",
    "            if floor == 80:\n",
    "                # TODO: 要 raise 一個 exception\n",
    "                \n",
    "    except '''TODO: 要用一個 exception 接''' as e:\n",
    "        print(e)\n",
    "        print(\"突破機關！\")\n",
    "        while floor:\n",
    "            floor -= 1\n",
    "            print(\"現在在 {} 樓\".format(floor))\n",
    "            \n",
    "            if floor == 5:\n",
    "                # TODO: 要 raise 一個 exception\n",
    "     \n",
    "# TODO: 用 try...except 把 slip(106) 包起來\n",
    "slip(106)"
   ]
  }
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