{
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  {
   "cell_type": "markdown",
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    "nbsphinx": "hidden"
   },
   "source": [
    "[prev: Exécuter son script](command-line.ipynb) | [home](../index.ipynb) | [next: Introduction aux fonctions](fonction-intro.ipynb)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Noms et variables\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Utiliser des variables pour être plus flexible"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "La même instruction, `print(a * 2)` , donne différents résultats selon la valeur de `a`.\n",
    "\n",
    "-> séparation entre opérations et données"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "toto\n",
      "tata\n",
      "42\n"
     ]
    }
   ],
   "source": [
    "a = 'to'\n",
    "print(a * 2)\n",
    "\n",
    "a = 'ta'\n",
    "print(a * 2)\n",
    "\n",
    "a = 21\n",
    "print(a * 2)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Un même nom peut être utilisé successivement pour différentes variables/valeurs sans contrainte de type."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Utiliser un nom inconnu est difficile"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "tags": [
     "raises-exception"
    ]
   },
   "outputs": [
    {
     "ename": "NameError",
     "evalue": "name 'inconnu' 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[2], line 1\u001b[0m\n\u001b[1;32m----> 1\u001b[0m \u001b[43minconnu\u001b[49m\n",
      "\u001b[1;31mNameError\u001b[0m: name 'inconnu' is not defined"
     ]
    }
   ],
   "source": [
    "inconnu"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'XXX'"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "inconnu = 'XXX'\n",
    "inconnu"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Qu'est-ce qu'un nom licite ?"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Il utilise seulement les caractères suivants\n",
    "\n",
    "- underscore : `_`\n",
    "- lettres minuscules : `[a-z]`\n",
    "- lettres majuscules : `[A-Z]`\n",
    "- nombres : `[0-9]`\n",
    "\n",
    "**MAIS** il ne commence pas par un nombre (`[0-9]`)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [],
   "source": [
    "# exemples qui marchent\n",
    "\n",
    "x = 2\n",
    "\n",
    "camion = 'vroum'\n",
    "\n",
    "HAUT = 'O'\n",
    "\n",
    "unnomlongmaispaslisible = 0\n",
    "\n",
    "un_nom_long_lisible = 1\n",
    "\n",
    "UnNomLongAussiLisible = 2\n",
    "\n",
    "_avec_une_patte_devant = 3\n",
    "\n",
    "__avec_des_longues_pattes_partout__ = 4"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "tags": [
     "raises-exception"
    ]
   },
   "outputs": [
    {
     "ename": "SyntaxError",
     "evalue": "invalid syntax (1202299578.py, line 2)",
     "output_type": "error",
     "traceback": [
      "\u001b[1;36m  Cell \u001b[1;32mIn[5], line 2\u001b[1;36m\u001b[0m\n\u001b[1;33m    allo? = 3\u001b[0m\n\u001b[1;37m        ^\u001b[0m\n\u001b[1;31mSyntaxError\u001b[0m\u001b[1;31m:\u001b[0m invalid syntax\n"
     ]
    }
   ],
   "source": [
    "# exemple qui marche pas\n",
    "allo? = 3"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "tags": [
     "raises-exception"
    ]
   },
   "outputs": [
    {
     "ename": "SyntaxError",
     "evalue": "cannot assign to expression here. Maybe you meant '==' instead of '='? (4131215381.py, line 2)",
     "output_type": "error",
     "traceback": [
      "\u001b[1;36m  Cell \u001b[1;32mIn[6], line 2\u001b[1;36m\u001b[0m\n\u001b[1;33m    deux-nom = 3\u001b[0m\n\u001b[1;37m    ^\u001b[0m\n\u001b[1;31mSyntaxError\u001b[0m\u001b[1;31m:\u001b[0m cannot assign to expression here. Maybe you meant '==' instead of '='?\n"
     ]
    }
   ],
   "source": [
    "# exemple qui marche pas\n",
    "deux-nom = 3"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "tags": [
     "raises-exception"
    ]
   },
   "outputs": [
    {
     "ename": "SyntaxError",
     "evalue": "invalid decimal literal (1058342908.py, line 2)",
     "output_type": "error",
     "traceback": [
      "\u001b[1;36m  Cell \u001b[1;32mIn[7], line 2\u001b[1;36m\u001b[0m\n\u001b[1;33m    0_commence_avec_zero = False\u001b[0m\n\u001b[1;37m     ^\u001b[0m\n\u001b[1;31mSyntaxError\u001b[0m\u001b[1;31m:\u001b[0m invalid decimal literal\n"
     ]
    }
   ],
   "source": [
    "# exemple qui marche pas\n",
    "0_commence_avec_zero = False"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**De plus**, Il ne doit pas être déjà réservé par le langage"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Voici les 35 mots-clefs de Python:\n",
      "\n",
      "- False        - None         - True         - and          - as           - assert       \n",
      "- async        - await        - break        - class        - continue     - def          \n",
      "- del          - elif         - else         - except       - finally      - for          \n",
      "- from         - global       - if           - import       - in           - is           \n",
      "- lambda       - nonlocal     - not          - or           - pass         - raise        \n",
      "- return       - try          - while        - with         - yield        \n"
     ]
    }
   ],
   "source": [
    "from keyword import kwlist\n",
    "\n",
    "width = 6\n",
    "\n",
    "print(f'Voici les {len(kwlist)} mots-clefs de Python:\\n')\n",
    "\n",
    "for i in range(0, len(kwlist), width):\n",
    "    for word in kwlist[i:i + width]:\n",
    "        print('-', word.ljust(12), end=' ')\n",
    "    print()\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "tags": [
     "raises-exception"
    ]
   },
   "outputs": [
    {
     "ename": "SyntaxError",
     "evalue": "invalid syntax (986342119.py, line 1)",
     "output_type": "error",
     "traceback": [
      "\u001b[1;36m  Cell \u001b[1;32mIn[9], line 1\u001b[1;36m\u001b[0m\n\u001b[1;33m    lambda = 123\u001b[0m\n\u001b[1;37m           ^\u001b[0m\n\u001b[1;31mSyntaxError\u001b[0m\u001b[1;31m:\u001b[0m invalid syntax\n"
     ]
    }
   ],
   "source": [
    "lambda = 123"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {
    "tags": []
   },
   "outputs": [],
   "source": [
    "lambda_ = 123"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Extra"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {
    "tags": [
     "raises-exception"
    ]
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "3\n"
     ]
    },
    {
     "ename": "TypeError",
     "evalue": "'str' object is not callable",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "Cell \u001b[1;32mIn[11], line 4\u001b[0m\n\u001b[0;32m      2\u001b[0m \u001b[38;5;28mprint\u001b[39m(\u001b[38;5;28mint\u001b[39m(\u001b[38;5;241m3.14\u001b[39m))\n\u001b[0;32m      3\u001b[0m \u001b[38;5;28mint\u001b[39m \u001b[38;5;241m=\u001b[39m \u001b[38;5;124m'\u001b[39m\u001b[38;5;124moups\u001b[39m\u001b[38;5;124m'\u001b[39m\n\u001b[1;32m----> 4\u001b[0m \u001b[38;5;28mprint\u001b[39m(\u001b[38;5;28;43mint\u001b[39;49m\u001b[43m(\u001b[49m\u001b[38;5;241;43m3.14\u001b[39;49m\u001b[43m)\u001b[49m)\n",
      "\u001b[1;31mTypeError\u001b[0m: 'str' object is not callable"
     ]
    }
   ],
   "source": [
    "# Attention : 'int', 'float', 'str' ne sont pas réservés !\n",
    "print(int(3.14))\n",
    "int = 'oups'\n",
    "print(int(3.14))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [],
   "source": [
    "int = type(1)  # un moyen de restaurer 'int'"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Exercice"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Jouer un peu avec les opérateurs `+`, `*` ...\n",
    "\n",
    "Essayer un exemple concret avec la conversion de température °C/°F [de formule $ Celsius = \\frac{5}{9}(Fahrenheit - 32) $](https://fr.wikipedia.org/wiki/Degr%C3%A9_Fahrenheit).\n",
    "\n",
    "Expérimenter l'utilisation du `print(nom)` pour voir le résultat de quelques calculs."
   ]
  }
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