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 OOP

Estimated time

20-45 minutes

Level of difficulty

Easy/Medium

1)Scenario

As you already know, a stack is a data structure realizing the so-called LIFO (Last In - First Out) model. It's easy and you've already grown perfectly accustomed to it.

Let's taste something new now. A queue is a data model characterized by the term FIFO: First In - Fist Out. Note: a regular queue (line) you know from shops or post offices works exactly in the same way - a customer who came first is served first too.

Your task is to implement the Queue class with two basic operations:

  • put(element), which puts an element at end of the queue;
  • get(), which takes an element from the front of the queue and returns it as the result (the queue cannot be empty to successfully perform it.)

Follow the hints:

  • use a list as your storage (just like we did in stack)
  • put() should append elements to the beginning of the list, while get() should remove the elements from the list's end;
  • define a new exception named QueueError (choose an exception to derive it from) and raise it when get() tries to operate on an empty list.

Complete the code we've provided in the editor. Run it to check whether its output is similar to ours.

Expected output

1 dog False Queue error


CODE:

class QueueError(IndexError):
    pass


class Queue:
    def __init__(self):
        self.queue = []

    def put(self, elem):
        self.queue.insert(0, elem)

    def get(self):
        if len(self.queue) > 0:
            elem = self.queue[-1]
            del self.queue[-1]
            return elem
        else:
            raise QueueError


que = Queue()
que.put(1)
que.put("dog")
que.put(False)
try:
    for i in range(4):
        print(que.get())
except:
    print("Queue error")

2)Scenario

Your task is to slightly extend the Queue class' capabilities. We want it to have a parameterless method that returns True if the queue is empty and False otherwise.

Complete the code we've provided in the editor. Run it to check whether it outputs a similar result to ours.

CODE:

class QueueError(IndexError):

    pass

class Queue:

    def __init__(self):

        self.queue = []

    def put(self,elem):

        self.queue.insert(0,elem)

    def get(self):

        if len(self.queue) > 0:

            elem = self.queue[-1]

            del self.queue[-1]

            return elem

        else:

            raise QueueError


class SuperQueue(Queue):

    def isempty(self):

        return len(self.queue) == 0


que = SuperQueue()

que.put(1)

que.put("dog")

que.put(False)

for i in range(4):

    if not que.isempty():

        print(que.get())

    else:

        print("Queue empty")



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