{
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   "source": [
    "[prev: Les conteneurs de base](data-structures.ipynb) | [home](../index.ipynb) | [next: Structuration du code](code-block.ipynb)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Structure de contrôle\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "- if (test) elif else\n",
    "    * conversion implicite en booléen\n",
    "- while (test) [break/continue] else\n",
    "- for (iter) [break/continue] else\n",
    "\n",
    "susucre : `a = x if cond else y`"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## IF - ELIF - ELSE\n",
    "\n",
    "<img width=50% src='http://upload.wikimedia.org/wikipedia/commons/thumb/d/d3/Cf-if-fr.svg/1000px-Cf-if-fr.svg.png'/>"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Structure de `if - elif -else`\n",
    "\n",
    "``` python\n",
    "# instruction avant le if\n",
    "\n",
    "if test_1:\n",
    "    # instruction A\n",
    "elif test_2:\n",
    "    # instruction B\n",
    "elif test_3:\n",
    "    # instruction C\n",
    "else:\n",
    "    # instruction D\n",
    "\n",
    "# instruction après le if\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "start\n",
      "travail\n",
      "end\n"
     ]
    }
   ],
   "source": [
    "print('start')\n",
    "\n",
    "a = 1\n",
    "\n",
    "if a == 1:\n",
    "    print('travail')\n",
    "\n",
    "print('end')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "start\n",
      "end\n"
     ]
    }
   ],
   "source": [
    "print('start')\n",
    "\n",
    "a = 2\n",
    "\n",
    "if a == 1:\n",
    "    print('travail')\n",
    "\n",
    "print('end')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<img width=50% src='http://upload.wikimedia.org/wikipedia/commons/thumb/8/8a/Cf-else-fr.svg/1000px-Cf-else-fr.svg.png'/>"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "start\n",
      "travail 1\n",
      "end\n"
     ]
    }
   ],
   "source": [
    "print('start')\n",
    "\n",
    "a = 1\n",
    "\n",
    "if a == 1:\n",
    "    print('travail 1')\n",
    "else:\n",
    "    print('travail 2')\n",
    "\n",
    "print('end')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "start\n",
      "travail 2\n",
      "end\n"
     ]
    }
   ],
   "source": [
    "print('start')\n",
    "\n",
    "a = 1\n",
    "\n",
    "if a == 2:\n",
    "    print('travail 1')\n",
    "else:\n",
    "    print('travail 2')\n",
    "\n",
    "print('end')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<img width=50% src='http://upload.wikimedia.org/wikipedia/commons/thumb/e/e9/Cf-elif-fr.svg/1000px-Cf-elif-fr.svg.png'/>"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "travail 1\n"
     ]
    }
   ],
   "source": [
    "a = 1\n",
    "\n",
    "if a == 1:\n",
    "    print('travail 1')\n",
    "elif a == 2:\n",
    "    print('travail 2')\n",
    "else:\n",
    "    print('dodo')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "travail 2\n"
     ]
    }
   ],
   "source": [
    "a = 2\n",
    "\n",
    "if a == 1:\n",
    "    print('travail 1')\n",
    "elif a == 2:\n",
    "    print('travail 2')\n",
    "else:\n",
    "    print('dodo')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "dodo\n"
     ]
    }
   ],
   "source": [
    "a = 3\n",
    "\n",
    "if a == 1:\n",
    "    print('travail 1')\n",
    "elif a == 2:\n",
    "    print('travail 2')\n",
    "else:\n",
    "    print('dodo')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## FOR\n",
    "\n",
    "En python, `for` permet d'itérer sur les éléments d'une séquence (ex: `list`, `tuple`, `dict`)."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "toto\n",
      "42\n",
      "3.14\n"
     ]
    }
   ],
   "source": [
    "ma_liste = ['toto', 42, 3.14]\n",
    "\n",
    "for elem in ma_liste:\n",
    "    print(elem)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "un\n",
      "2\n",
      "trois\n"
     ]
    }
   ],
   "source": [
    "mon_dict = {'un': 42, 2: 'bonjour', 'trois': 3.14}\n",
    "\n",
    "for elem in mon_dict:\n",
    "    print(elem)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "p\n",
      "y\n",
      "t\n",
      "h\n",
      "o\n",
      "n\n"
     ]
    }
   ],
   "source": [
    "for elem in 'python':\n",
    "    print(elem)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Structure de `for - continue / break - else`\n",
    "\n",
    "``` python\n",
    "# instruction avant le for\n",
    "\n",
    "for elem in sequence:\n",
    "    # debut des instructions\n",
    "    if test_break:\n",
    "        # on arrete tout\n",
    "        break\n",
    "    if test_continue:\n",
    "        # on passe à l'itération suivante\n",
    "        continue\n",
    "    # suite des instructions\n",
    "    # pas vue si continue\n",
    "else:\n",
    "    # executer si on est sorti de la boucle sans break\n",
    "\n",
    "# instruction après le for\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "tout s'est bien passé\n",
      "[0, 2, 4, 6, 8]\n"
     ]
    }
   ],
   "source": [
    "#liste = range(15)\n",
    "liste = range(10)\n",
    "result = []\n",
    "\n",
    "for elem in liste:\n",
    "    if elem > 10:\n",
    "        result = 'interdit de dépasser 10'\n",
    "        break\n",
    "    if elem % 2:\n",
    "        # ignorer les impairs\n",
    "        continue\n",
    "    result.append(elem)  # un peu comme 'result += [elem]' mais bien mieux\n",
    "else:\n",
    "    print(\"tout s'est bien passé\")\n",
    "\n",
    "print(result)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**Remarque**  Ce dernier exemple présente de gros défauts:\n",
    "\n",
    "  - changer la nature de `result` selon le contexte\n",
    "  - `else: print(...)` est un mode de communication très faible"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## WHILE\n",
    "\n",
    "<img width=30% src='http://upload.wikimedia.org/wikipedia/commons/thumb/5/51/Cf-while-fr.svg/1000px-Cf-while-fr.svg.png'/>"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Structure de `while - continue / break - else`\n",
    "\n",
    "``` python\n",
    "# instruction avant le while\n",
    "\n",
    "while test_boucle:\n",
    "    # debut des instructions\n",
    "    if test_break:\n",
    "        # on arrete tout\n",
    "        break\n",
    "    if test_continue:\n",
    "        # on passe à l'itération suivante\n",
    "        continue\n",
    "    # suite des instructions\n",
    "    # pas vue si continue\n",
    "else:\n",
    "    # executer si on est sorti de la boucle sans break\n",
    "\n",
    "# instruction après le while\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1 2 3 4 5 6 7 8 9 10 "
     ]
    }
   ],
   "source": [
    "# compteur\n",
    "\n",
    "a = 0\n",
    "\n",
    "while a < 10:\n",
    "    a += 1\n",
    "    print(a, end=' ')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "2 4 6 8 10 "
     ]
    }
   ],
   "source": [
    "# compteur pair\n",
    "\n",
    "a = 0\n",
    "\n",
    "while a < 10:\n",
    "    a += 1\n",
    "    if a % 2:\n",
    "        continue\n",
    "    print(a, end=' ')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {},
   "outputs": [],
   "source": [
    "def indice(liste, valeur):\n",
    "    \"renvoie le premier indice tq liste[indice] == valeur\"\n",
    "    i = 0\n",
    "    \n",
    "    while i < len(liste):\n",
    "        if liste[i] == valeur:\n",
    "            result = i\n",
    "            break\n",
    "        i += 1\n",
    "    else:\n",
    "        result = None\n",
    "        \n",
    "    return result\n",
    "\n",
    "\n",
    "ma_liste = ['zero', 'un', 'deux', 'trois']"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "2"
      ]
     },
     "execution_count": 15,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "indice(ma_liste, 'deux')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {},
   "outputs": [],
   "source": [
    "indice(ma_liste, 'quatre')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "En pratique, on préférera l'utilisation du `for` (éventuellement couplé à un `if`) qui ne risque pas de partir dans des boucles infinies.\n",
    "\n",
    "Par exemple, le code suivant tournera à l'infini (et on n'aime pas ça) :\n",
    "```python\n",
    "a = 0\n",
    "\n",
    "while a < 10:\n",
    "    if a % 2:\n",
    "        continue\n",
    "    print(a, end=' ')\n",
    "    a += 1\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "0 2 4 6 8 10 "
     ]
    }
   ],
   "source": [
    "# compteur pair\n",
    "\n",
    "for a in range(25):\n",
    "    if a > 10:\n",
    "        break\n",
    "    if a % 2:\n",
    "        continue\n",
    "    print(a, end=' ')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Exercice"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "- [Conversion de secondes (étape 2)](../exercises/exercises.ipynb#Exercice-3-:-conversion-de-secondes)\n",
    "- [Compte occurences (étape 1)](../exercises/exercises.ipynb#Exercice-5-:-compte-occurences)\n",
    "- [Suite de Collatz](../exercises/exercises.ipynb#Exercice-6-:-suite-de-Collatz)"
   ]
  }
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