Question

# 1. After studying the Stack class and testStack() functions in stack.py # complete the Queue class below (and test it with the testQueue function) # # 2. Afer studying and testing the Circle class in circle.py, # complete the Rectangle class below (and test it with the testRectangle function) # # # 3. SUBMIT THIS ONE FILE, with your updates, TO ICON. # # # NOTE: you may certainly add more tests to the test functions if you want!! ##### # 1. Complete the Queue class (following the style of the Stack class) # # A queue is similar to a stack but a bit different. # # # # # A queue is a collection of items supporting three operations: - enqueue (item): add item to the front of the queue - dequeue (): removes the "last" item from the queue (the one that's been in the queue the longest) and returns it - size(): returns the number of items currently in the queue # # Note: stacks are "LIFO" (last-in-first-out) while queues are "FIFO" (first-in-first-out) class Queue: def __init__(self): self.items = pass def dequeue (self): return self[:-1] def size(self): return len(self.items) def enqueue (self, item): return self.enqueue(item) def testQueue(): q = Queue () print("Created an empty Queue") print("Size is now: {}".format(q.size())) print("Enqueue-ing: 3, then 'hi', then 99") q.enqueue (3) 9. enqueue ob ("hi") q.enqueue ( 99 print("Size is now: {}".format(q.size())) print("Dequeue-ing ...") print(q.dequeue()) print("Size is now: {}", format(q.size())) print("Dequeue-ing ...") print(q.dequeue()) print("Size is now: {}".format(q.size())) print("Enqueue-ing: [1,2]") q.enqueue print("Size is now: {}".Format(q.size())) print("Dequeue-ing...") print(q.dequeue()) print("Size is now: {}".format(q.size())) print("Dequeue-ing ...") print(q.dequeue ( ) ) print("Size is now: {}".format(q.size())) print(q.dequeue()) print("Size is now: {}".format(q.size()))
help finish Queue, don't think I have the right thing.

Answer 1

Hi,

Hope you are doing fine. You have done a great job with the code of Stack and even queue class. I see that you need help with the queue. In the code, you have only made a few eerors in the class definitions of the Queue class. I have corrected the code and have executed it successfully in jupyter notebook. The code has been explained using comments that have been highlighted in bold. I haven't put any explanation for the testQueue() class as the print statements give you the whole picture. Also, have a look at the code snippet and sample output get a clearer insight on the indentation and output of the code. Also note that I haven't made any new methods and have corrected only the existing ones.

Program:

class Queue:
def __init__(self):
#initializing empty queue
self.items=[]
  
def dequeue(self):
#checking if the queue is not empty
if(len(self.items)>0):
#we delete the first element of queue as it follows FIFO priciple
front=self.items.pop(0)
#returning the deleted element
return front
#if the queue is empty
else:
print("Error: you can't dequeue from an empty queue")
  
#gives the size of queue
def size(self):
return len(self.items)
  
#adds elements to the queue
def enqueue(self,item):
#we simply append the item to the list.
self.items.append(item)

#Testing class
def testQueue():
q=Queue()
print("Created an empty Queue")
print("Size is now: {}".format(q.size()))
print("Enqueue-ing: 3, then 'hi', then 99")
q.enqueue(3)
q.enqueue("hi")
q.enqueue(99)
print("Size is now: {}".format(q.size()))
print("Dequeue-ing ...")
print(q.dequeue())
print("Size is now: {}".format(q.size()))
print("Dequeue-ing ...")
print(q.dequeue())
print("Size is now: {}".format(q.size()))
print("Enqueue-ing: [1,2]")
#the list [1,2] is taken as one element and not two.
q.enqueue([1,2])
print("Size is now: {}".format(q.size()))
print("Dequeue-ing ...")
print(q.dequeue())
print("Size is now: {}".format(q.size()))
print("Dequeue-ing ...")
print(q.dequeue())
print("Size is now: {}".format(q.size()))
print(q.dequeue())
print("Size is now: {}".format(q.size()))

testQueue()

Executable code snippet:

In [10]: class Queue: def __init__(self): #initializing empty queue self.items=[ def dequeue (self): #checking if the queue is not empty if(len(self.items)>0): #we delete the first element of queue as it follows FIFO priciple front=self.items.pop() #returning the deleted element return front #if the queue is empty else: print("Error: you can't dequeue from an empty queue") #gives the size of queue def size (self): return len(self.items) #adds elements to the queue def enqueue (self, item): #we simply append the item to the list. self.items.append(item) #Testing class def testQueue(): q=Queue) print("Created an empty Queue") print("Size is now: {}".format(q.size()) print("Enqueue-ing: 3, then 'hi', then 99") q.enqueue (3) q.enqueue ("hi") q.enqueue (99) print("Size is now: {}".format(q.size()) print("Dequeue-ing ...") print(q.dequeue () print("Size is now: {}".format(q.size()) print("Dequeue-ing ...") print(q.dequeue) print("Size is now: {}".format(q.size()) print("Enqueue-ing: [1,2]") #the list [1,2] is taken as one element and not two. q.enqueue ([1,2]) print("Size is now: {}".format(q.size()) print("Dequeue-ing ...") print(q.dequeue () print("Size is now: {}".format(q.size()) print("Dequeue-ing ...") print(q.dequeue) print("Size is now: {}".format(q.size()) print(q.dequeue () print("Size is now: {}".format(q.size()) testQueue)

Sample output:

Created an empty Queue Size is now: 0 Enqueue-ing: 3, then 'hi', then 99 Size is now: 3 Dequeue-ing ... 3 size is now: 2 Dequeue-ing .. hi size is now: 1 Enqueue-ing: [1,2] Size is now: 2 Dequeue-ing 99 Size is now: 1 Dequeue-ing [1, 2] Size is now: 0 Error: you can't dequeue from an empty queue None Size is now: 0