# CP Python: Seance 5

## 1. Théorie

### Recherche dichotomique

| Linear Search | Binary Search |
| -------- | -------- |
| `linear_search('mango',lst)` <img src="https://i.imgur.com/oIDFFRs.png" width="1600"> | <img src="https://i.imgur.com/JSAwDdo.png" width="800"> <img src="https://i.imgur.com/uQtV7x5.png" width="900">
| $\Delta$`t_execution` proportionnel à $n$ => $O(n)$ |$\Delta$`t_execution`proportionnel à $log_2(n)$ => $O(log (n))$
| | - [Video 1](https://www.youtube.com/watch?v=DnvWAd-RGhk) - [Video 2](https://www.youtube.com/watch?v=t914IvpnTWQ)

### Fichiers

* Pourquoi `close` est nécessaire ?

 file = open ( name, "r" )
 for line in file:
     print(line)
 file.close () 

* Comment fermer le fichier implicitement ?

with open ( name, "w" ) as file:
            # opérations sur fichier file ...

* `strip()`, `split()`, `int()`, `tuple()`, `float()`

<div style="text-align:center">
<img src="https://i.imgur.com/Ixpiwnh.png" width=500>
</div>

### Exceptions
* A quoi ça sert d'intercepter une Erreur (Exception) ?

    num = input ( "Provide a number: " )
    try:
        # Si num == 0, alors Python ordonne d'utiliser raise ValueError
        print ( 1 / int(num) )
    except:
        print ( "Error doing calculation" )
    operation_importante()

    def is_number ( text, n ):
        try:
            value = int(text)
            return value >= 0 and value <= n
        except ValueError:
            return False

* A quoi ça sert de lancer une Erreur (Exception) ?

    def askAge ():
        age = int(input( "Provide your age: " ))
        if age < 0 or age >= 150:
            raise ValueError ( "Age out of range" )
        return age

* Fichiers & Exceptions

    try:
        with open ( name, "w" ) as file:
        # opérations sur fichier file 
    except:
        # faire qqch en cas d'erreur

* Erreur spécifique ? https://docs.python.org/3/library/exceptions.html
* exception `ValueError`
* exception `DivisionByZero`
* exception `IndexError`
* lst[i] mais la longueur de lst est plus petite que i p.ex.
* exception `FileNotFound`
* exception `OSError`

## 2. Exercices

1. __Binary Search__:

* Résoudre la question 3 et 4 de la Session 5, disponible ici: https://syllabus-interactif.info.ucl.ac.be/syllabus/info1-exercises/PART_II/MISSION_5/preparation

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2. __Interrogation__:
* Recopier votre code lié à l'interrogation dans un fichier `interro_student.py`. Si vous avez plusieurs solutions, mettez les toutes.
* Résoudre une variante de `trouver_doublon`
* Ecrire une fonction `trouver_plus_long_PIN` qui permet de retrouver la personne dont le mot de passe est le plus sécurisé, parmi des mots de passe exclusivement numériques, autrement dit le plus long.
* Autrement dit, si la liste `pin_list = [('Kim','Mens',1232445),('Olivier','Pecheur',8349),('Aragorn','Premier Du Nom',101)]` est donnée en argument, `trouver_plus_long_PIN(pin_list)` devra retourner le string `"Kim Mens"`
* Contrainte: Veuillez ré-utiliser la fonction `count_digits` :wink:

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3. [Session 6: Q* Hogwarts - Quidditch](https://syllabus-interactif.info.ucl.ac.be/syllabus/info1-exercises/PART_II/MISSION_6/complement)
- The scores list would be provided as a file. The content of this file would follow this format:
- Two first lines: Names of the team
- Lines after: Team_scoring points
- In case of error, just raise it.
- Remember that the catch of the golden snitch (150 points) means the end of the match.
- Implement the function `referee(score_file)` in Python.

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4. [Session 6 : Q* Sauvegarde](https://syllabus-interactif.info.ucl.ac.be/syllabus/info1-exercises/PART_II/MISSION_6/complement)

* You have to create two function, one to save the data and one to load the data previously saved.
* You are free to store the data like you want in the file, but putting one integer per line is probably the easiest.
* If there is no file to load when using the function `load_data` (for exemple, the player starts a new game), you must raise a FileNotFoundError.
* The two functions will have these definition :

#save the 4 integer to the file named filename
def save_data(filename, life, mana, position_x, position_y):


#return a tuple containing (life, mana, position_x, position_y) previously saved
def load_data(filename):

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### Resources de la séance passée:
* Le document principal https://hackmd.io/@Tb5Z2PdeRLSnkxJEsjcLXg/rk5z1u_5v
* Le repl: https://repl.it/@GuillaumeGst/CP-Python-Seance-4-1