exercises.md

Exercise 1 - List manipulation

Question 1

Write a function call word_letter_position that takes three parameters :

• a list of string
• a letter (string)
• a position (integer)

This function must return all the words contained in the input list that contain the letter at the position specified.

You can test the following exercise with this input list :

'rickon', 'theon', 'rorbert', 'cersei', 'tywin', 'jaime',
'tyrion', 'shae', 'bronn', 'lancel', 'joffrey', 'sandor',
'varys', 'renly', 'a' ]

Example: word_letter_position(input_list, 'y', 1) will return ['tywin', 'tyrion']

Question 2

Write a parametrized unit test with pytest (see pytest.mark.parametrize) that tests this function with all the corner cases possibles.

Exercise 2 - Dictionary manipulation

You receive a dictionary that can contain dictionaries that can contains dictionaries etc... (they are called nested dictionaries).

Question 1

Write a function that takes into parameters this dictionary and a string. The string will be under the form "key1.key2.key3...". This function will return the value associated to the key passed in parameters if it exists, and raise an exception otherwise.

Example :

mydict = {
  "a": {
      "b": 33
    }
}
get_value(mydict, "a.b")  # will return 33

Question 2

Write a parametrized unit test with pytest (see pytest.mark.parametrize) that tests this function with all the corner cases possibles. Also write a unit test testing if the function correctly raises an exception if the key requested is not found in the dictionary.

Exercice 3 - Class methods & Namedtuple

Question 1

Create a namedtuple object called Card containing two attributes: rank and suits. Then create a list of 52 Card objects, one for each rank and suit that can be found in some french decks : 2,3...10, J, Q, K, A for the ranks; and spades, diamonds, hearts and clubs for the suits.

Question 2

Create a class Deck containing the list created previously as an attribute (set in the initialization method). Write custom methods for this class such that the following assertions return True:

deck = Deck()

assert len(deck) == 52
assert isinstance(deck[0], Card)

Question 3

Write a method card_value which returns the value of the card passed in parameter, considering that spades > diamonds > hearts > clubs. For example, the 2 of spades will have a greater value than the 2 of diamonds, which will have a greater value than the 2 of hearts etc...

• 2 of clubs: 0

• 2 of hearts: 1

• 2 of diamonds: 2

• 2 of spades: 3

• 3 of clubs: 4

  ⋮

• As of spades: 51

Exercise 4 - base64 and string manipulation

You receive a string encoded in base64. You know that once decoded, this string has the following format :

machine<id>?:<name>@<vendor>?:<password>@<year>

where id and year are integers, name and vendor are alphanumerical strings, and password is a string that can contain alphanumerical values, integers or the following special characters: .?@!:.

Question 1

Write a function that can decode the encoded string and return the password.

You can test your function with the following inputs :

bWFjaGluZTE/OmJvYkBtYW1hem9uPzpzaW1wbGVwYXNzd29yZDFAMjAzMg==    # should output simplepassword1
bWFjaGluZTI/OmFsaWNlQGFsaWJvdWJvdT86cFJmP2dsMTJATUAyMDMy    # should output pRf?gl12@M
bWFjaGluZTM/Om1hcnRpbkBzbmFjPzptZHA/OmJiOEAyMDMz    # should output mdp?:bb8
bWFjaGluZTQ/OmVsb0BkYXJweT86QGM/NEBAZ3JyPzpAMjAzMw==    # should output @c?4@@grr?:

Question 2

Write a parametrized unit test with pytest (see pytest.mark.parametrized) testing the previous function with the given inputs.

Exercise 5 - decorators

Question 1

Write a multiply function that multiply two numbers and return the result.

Write a decorator that cache the parameters and result of each call to multiply into a global dictionary.

Before each call to multiply, verify if it was already called before with the same parameters by looking at the dictionary. If it was already, just return the result stored in the dictionary and don't call multiply.

Look of the global dictionary:

cache = {
 (1, 2): 2,
 (3, 5): 5,
 ...
}

Question 2

Write a decorator that limit the number of executions authorized for a function. This decorator will take a parameter nb_executions that represent the max of executions authorized. If a decorated function was called too many times, raise a customized exception called LimitExcedeed.

Exercise 6 - Flask decorator

In this exercise, we're going to 'mimick' Flask decorators in a very simplified way.

Create a class App such that the following code registers the decorated functions into a route_dict dictionary.

For example, for this code:

app = App()

@app.route("/", methods=["GET", "POST"])
def index():
    return "Welcome"

@app.route("/new_user", methods=["POST"])
def user():
    print("Added user")

print(app.route_dict)

app.route_dict will look like:

{
   'GET': [{'/': 'index'}],
   'POST': [{'/': 'index'}, {'/new_user': 'user'}]
}