{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {
    "nbsphinx": "hidden"
   },
   "source": [
    "[prev: Noms et objets non immuables\n",
    "](naming-vs-pointer.ipynb) | [home](../index.ipynb) | [next: Listes en intention](list-comprehension.ipynb)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Gérer les exceptions\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Qu'est-ce donc ?\n",
    "\n",
    "Une exception est levée quand une erreur est commise"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "tags": [
     "raises-exception"
    ]
   },
   "outputs": [
    {
     "ename": "NameError",
     "evalue": "name 'nexistepas' is not defined",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mNameError\u001b[0m                                 Traceback (most recent call last)",
      "Cell \u001b[1;32mIn[1], line 1\u001b[0m\n\u001b[1;32m----> 1\u001b[0m \u001b[43mnexistepas\u001b[49m\n",
      "\u001b[1;31mNameError\u001b[0m: name 'nexistepas' is not defined"
     ]
    }
   ],
   "source": [
    "nexistepas"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "tags": [
     "raises-exception"
    ]
   },
   "outputs": [
    {
     "ename": "ZeroDivisionError",
     "evalue": "division by zero",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mZeroDivisionError\u001b[0m                         Traceback (most recent call last)",
      "Cell \u001b[1;32mIn[2], line 1\u001b[0m\n\u001b[1;32m----> 1\u001b[0m \u001b[38;5;241;43m2\u001b[39;49m\u001b[43m \u001b[49m\u001b[38;5;241;43m/\u001b[39;49m\u001b[43m \u001b[49m\u001b[38;5;241;43m0\u001b[39;49m\n",
      "\u001b[1;31mZeroDivisionError\u001b[0m: division by zero"
     ]
    }
   ],
   "source": [
    "2 / 0"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "tags": [
     "raises-exception"
    ]
   },
   "outputs": [
    {
     "ename": "TypeError",
     "evalue": "can only concatenate str (not \"int\") to str",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "Cell \u001b[1;32mIn[3], line 1\u001b[0m\n\u001b[1;32m----> 1\u001b[0m \u001b[38;5;124;43m'\u001b[39;49m\u001b[38;5;124;43mun\u001b[39;49m\u001b[38;5;124;43m'\u001b[39;49m\u001b[43m \u001b[49m\u001b[38;5;241;43m+\u001b[39;49m\u001b[43m \u001b[49m\u001b[38;5;241;43m2\u001b[39;49m\n",
      "\u001b[1;31mTypeError\u001b[0m: can only concatenate str (not \"int\") to str"
     ]
    }
   ],
   "source": [
    "'un' + 2"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "tags": [
     "raises-exception"
    ]
   },
   "outputs": [
    {
     "ename": "IndexError",
     "evalue": "string index out of range",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mIndexError\u001b[0m                                Traceback (most recent call last)",
      "Cell \u001b[1;32mIn[4], line 1\u001b[0m\n\u001b[1;32m----> 1\u001b[0m \u001b[38;5;124;43m'\u001b[39;49m\u001b[38;5;124;43mbonjour\u001b[39;49m\u001b[38;5;124;43m'\u001b[39;49m\u001b[43m[\u001b[49m\u001b[38;5;241;43m9\u001b[39;49m\u001b[43m]\u001b[49m\n",
      "\u001b[1;31mIndexError\u001b[0m: string index out of range"
     ]
    }
   ],
   "source": [
    "'bonjour'[9]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "tags": [
     "raises-exception"
    ]
   },
   "outputs": [
    {
     "ename": "KeyError",
     "evalue": "'deux'",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mKeyError\u001b[0m                                  Traceback (most recent call last)",
      "Cell \u001b[1;32mIn[5], line 1\u001b[0m\n\u001b[1;32m----> 1\u001b[0m \u001b[43m{\u001b[49m\u001b[38;5;124;43m'\u001b[39;49m\u001b[38;5;124;43mun\u001b[39;49m\u001b[38;5;124;43m'\u001b[39;49m\u001b[43m:\u001b[49m\u001b[43m \u001b[49m\u001b[38;5;241;43m1\u001b[39;49m\u001b[43m}\u001b[49m\u001b[43m[\u001b[49m\u001b[38;5;124;43m'\u001b[39;49m\u001b[38;5;124;43mdeux\u001b[39;49m\u001b[38;5;124;43m'\u001b[39;49m\u001b[43m]\u001b[49m\n",
      "\u001b[1;31mKeyError\u001b[0m: 'deux'"
     ]
    }
   ],
   "source": [
    "{'un': 1}['deux']"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Le *Traceback* permet de suivre l'imbrication des appels au moment de l'erreur"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "tags": [
     "raises-exception"
    ]
   },
   "outputs": [
    {
     "ename": "ZeroDivisionError",
     "evalue": "division by zero",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mZeroDivisionError\u001b[0m                         Traceback (most recent call last)",
      "Cell \u001b[1;32mIn[6], line 13\u001b[0m\n\u001b[0;32m     10\u001b[0m \u001b[38;5;28;01mdef\u001b[39;00m \u001b[38;5;21mf3\u001b[39m(x):\n\u001b[0;32m     11\u001b[0m     \u001b[38;5;28;01mreturn\u001b[39;00m f2(x) \u001b[38;5;241m/\u001b[39m \u001b[38;5;241m3\u001b[39m\n\u001b[1;32m---> 13\u001b[0m \u001b[43mf3\u001b[49m\u001b[43m(\u001b[49m\u001b[38;5;241;43m1\u001b[39;49m\u001b[43m)\u001b[49m\n",
      "Cell \u001b[1;32mIn[6], line 11\u001b[0m, in \u001b[0;36mf3\u001b[1;34m(x)\u001b[0m\n\u001b[0;32m     10\u001b[0m \u001b[38;5;28;01mdef\u001b[39;00m \u001b[38;5;21mf3\u001b[39m(x):\n\u001b[1;32m---> 11\u001b[0m     \u001b[38;5;28;01mreturn\u001b[39;00m \u001b[43mf2\u001b[49m\u001b[43m(\u001b[49m\u001b[43mx\u001b[49m\u001b[43m)\u001b[49m \u001b[38;5;241m/\u001b[39m \u001b[38;5;241m3\u001b[39m\n",
      "Cell \u001b[1;32mIn[6], line 8\u001b[0m, in \u001b[0;36mf2\u001b[1;34m(x)\u001b[0m\n\u001b[0;32m      7\u001b[0m \u001b[38;5;28;01mdef\u001b[39;00m \u001b[38;5;21mf2\u001b[39m(x):\n\u001b[1;32m----> 8\u001b[0m     \u001b[38;5;28;01mreturn\u001b[39;00m \u001b[43mf1\u001b[49m\u001b[43m(\u001b[49m\u001b[43mx\u001b[49m\u001b[43m)\u001b[49m \u001b[38;5;241m/\u001b[39m \u001b[38;5;241m2\u001b[39m\n",
      "Cell \u001b[1;32mIn[6], line 5\u001b[0m, in \u001b[0;36mf1\u001b[1;34m(x)\u001b[0m\n\u001b[0;32m      4\u001b[0m \u001b[38;5;28;01mdef\u001b[39;00m \u001b[38;5;21mf1\u001b[39m(x):\n\u001b[1;32m----> 5\u001b[0m     \u001b[38;5;28;01mreturn\u001b[39;00m \u001b[43mf0\u001b[49m\u001b[43m(\u001b[49m\u001b[43mx\u001b[49m\u001b[43m)\u001b[49m \u001b[38;5;241m/\u001b[39m \u001b[38;5;241m1\u001b[39m\n",
      "Cell \u001b[1;32mIn[6], line 2\u001b[0m, in \u001b[0;36mf0\u001b[1;34m(x)\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[38;5;28;01mdef\u001b[39;00m \u001b[38;5;21mf0\u001b[39m(x):\n\u001b[1;32m----> 2\u001b[0m     \u001b[38;5;28;01mreturn\u001b[39;00m \u001b[43mx\u001b[49m\u001b[43m \u001b[49m\u001b[38;5;241;43m/\u001b[39;49m\u001b[43m \u001b[49m\u001b[38;5;241;43m0\u001b[39;49m\n",
      "\u001b[1;31mZeroDivisionError\u001b[0m: division by zero"
     ]
    }
   ],
   "source": [
    "def f0(x):\n",
    "    return x / 0\n",
    "\n",
    "def f1(x):\n",
    "    return f0(x) / 1\n",
    "\n",
    "def f2(x):\n",
    "    return f1(x) / 2\n",
    "\n",
    "def f3(x):\n",
    "    return f2(x) / 3\n",
    "\n",
    "f3(1)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Il est possible d'émettre soit même une exception pour signaler une erreur."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [],
   "source": [
    "def fonction_qui_n_aime_pas_toto(valeur):\n",
    "    \"\"\" affiche valeur\n",
    "    Je n'aime pas Toto, donc 'toto' est une valeur interdite !\n",
    "    \"\"\"\n",
    "    if valeur == 'toto':\n",
    "        raise ValueError(\"T'es pas beau, toto !\")  # pensez à mettre un message utile...\n",
    "    print(valeur)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "tata\n"
     ]
    }
   ],
   "source": [
    "fonction_qui_n_aime_pas_toto('tata')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "tags": [
     "raises-exception"
    ]
   },
   "outputs": [
    {
     "ename": "ValueError",
     "evalue": "T'es pas beau, toto !",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mValueError\u001b[0m                                Traceback (most recent call last)",
      "Cell \u001b[1;32mIn[9], line 1\u001b[0m\n\u001b[1;32m----> 1\u001b[0m \u001b[43mfonction_qui_n_aime_pas_toto\u001b[49m\u001b[43m(\u001b[49m\u001b[38;5;124;43m'\u001b[39;49m\u001b[38;5;124;43mtoto\u001b[39;49m\u001b[38;5;124;43m'\u001b[39;49m\u001b[43m)\u001b[49m\n",
      "Cell \u001b[1;32mIn[7], line 6\u001b[0m, in \u001b[0;36mfonction_qui_n_aime_pas_toto\u001b[1;34m(valeur)\u001b[0m\n\u001b[0;32m      2\u001b[0m \u001b[38;5;250m\u001b[39m\u001b[38;5;124;03m\"\"\" affiche valeur\u001b[39;00m\n\u001b[0;32m      3\u001b[0m \u001b[38;5;124;03mJe n'aime pas Toto, donc 'toto' est une valeur interdite !\u001b[39;00m\n\u001b[0;32m      4\u001b[0m \u001b[38;5;124;03m\"\"\"\u001b[39;00m\n\u001b[0;32m      5\u001b[0m \u001b[38;5;28;01mif\u001b[39;00m valeur \u001b[38;5;241m==\u001b[39m \u001b[38;5;124m'\u001b[39m\u001b[38;5;124mtoto\u001b[39m\u001b[38;5;124m'\u001b[39m:\n\u001b[1;32m----> 6\u001b[0m     \u001b[38;5;28;01mraise\u001b[39;00m \u001b[38;5;167;01mValueError\u001b[39;00m(\u001b[38;5;124m\"\u001b[39m\u001b[38;5;124mT\u001b[39m\u001b[38;5;124m'\u001b[39m\u001b[38;5;124mes pas beau, toto !\u001b[39m\u001b[38;5;124m\"\u001b[39m)  \u001b[38;5;66;03m# pensez à mettre un message utile...\u001b[39;00m\n\u001b[0;32m      7\u001b[0m \u001b[38;5;28mprint\u001b[39m(valeur)\n",
      "\u001b[1;31mValueError\u001b[0m: T'es pas beau, toto !"
     ]
    }
   ],
   "source": [
    "fonction_qui_n_aime_pas_toto('toto')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## De nombreuses exceptions sont définies de base\n",
    "\n",
    "https://docs.python.org/2/library/exceptions.html#exception-hierarchy"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## try / except / else /finally\n",
    "\n",
    "Il est possible de 'sécuriser' une portion de code. Voire même d'intégrer l'erreur dans la logique du code.\n",
    "\n",
    "``` python\n",
    "try:\n",
    "    # bloc d'instruction dont on veux contrôler les exceptions émises\n",
    "except ExceptionType1 as err1:\n",
    "    # Traitement de err1\n",
    "    # Typiquement:\n",
    "    #    - on a une solution de repli dans le cas de err1\n",
    "    #    OU\n",
    "    #    - on sauve les meubles et on fait rebondir err1 (ou une nouvelle erreur)\n",
    "except ExceptionType2 as err2:\n",
    "    # Traitement de err2\n",
    "    # ...\n",
    "except ExceptionType3 as err3:\n",
    "    # Traitement de err3\n",
    "    # ...\n",
    "else:\n",
    "    # Si aucune exception n'est émise dans le try\n",
    "    # alors ce bloc est exécuté\n",
    "finally:\n",
    "    # Ce bloc sera exécuté quoi qu'il arrive\n",
    "```"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Exercices"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Ecrire une fonction `get(obj, index, default)` avec le même comportement que `dict.get()` mais qui marche aussi bien pour les dict ou les listes .\n",
    "\n",
    "Ecrire une fonction `map_with_default(function, sequence, default)` qui marche comme `map(function, sequence)` sauf que si une erreur est produite par `function` lors de son évaluation, l'erreur n'est pas propagée. A la place, la valeur manquante est assignée à `default`."
   ]
  }
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