Question: PYTHON. THE CODE DOESN'T WORK FOR THE LAST TEST CASE. Please review and change it! Circular, Array-backed Queue Overview For this assignment you will implement
PYTHON. THE CODE DOESN'T WORK FOR THE LAST TEST CASE. Please review and change it!
Circular, Array-backed Queue
Overview
For this assignment you will implement a circular, array-backed queue data structure.
In the following class, which you are to complete, the backing array will be created and populated with Nones in the __init__ method, and the head and tailindexes set to sentinel values (you shouldn't need to modify __init__). Enqueueing and Dequeueing items will take place at the tail and head, with tail and head tracking the position of the most recently enqueued item and that of the next item to dequeue, respectively. To simplify testing, your implementation should make sure that when dequeuing an item its slot in the array is reset to None, and when the queue is emptied its head and tail attributes should be set to -1.
Because of the fixed size backing array, the enqueue operation is defined to raise a RuntimeError when the queue is full the same exception should be raised when dequeue is called on an empty queue.
Finally, the resize method will allow the array underlying the queue to be increased in size. It is up to you how to implement this (you can either leave the elements in their current positions, though this may require "unwrapping" elements, or you can simply move all elements towards the front of the array). You may assume that resize will only be called with a value greater than the current length of the underlying array.
In [13]:
class Queue:
def __init__(self, limit=10):
self.data = [None] * limit
self.head = -1
self.tail = -1
def enqueue(self, val):
if self.head-self.tail==1:
raise RuntimeError
if len(self.data)-1 == self.tail and self.head == 0:
raise RuntimeError
if self.head == -1 and self.tail == -1:
self.data[0] = val
self.head = 0
self.tail = 0
else:
if len(self.data)-1 == self.tail and self.head !=0:
self.tail = -1
self.data[self.tail+1]=val
self.tail=self.tail+1
def dequeue(self):
if self.head == self.tail:
temp = self.head
self.head = -1
self.tail = -1
return self.data[temp]
if self.head == -1 and self.tail==-1:
raise RuntimeError
if self.head != len(self.data):
ret = self.data[self.head]
self.data[self.head]=None
self.head = self.head + 1
else:
self.head = 0
ret = self.data[self.head]
self.data[self.head]=None
self.head = self.head+1
return ret
def resize(self, newsize):
assert(len(self.data) < newsize)
newdata = [None]* newsize
head = self.head
current = self.data[head]
count = 0
while current != None:
newdata[count]=current
count+=1
if count !=0 and head==self.tail:
break
if head != len(self.data)-1:
head=head+1
current = self.data[head]
else:
head=0
current=self.data[head]
self.data=newdata
self.head=0
self.tail=count-1
def empty(self):
if self.head == -1 and self.tail == -1:
return True
return False
def __bool__(self):
return not self.empty()
def __str__(self):
if not(self):
return ''
return ', '.join(str(x) for x in self)
def __repr__(self):
return str(self)
def __iter__(self):
head = self.head
current = self.data[head]
count=0
while current != None:
yield current
count+=1
if count != 0 and head==self.tail:
break
if head != len(self.data)-1:
head=head+1
current = self.data[head]
else:
head=0
current = self.data[head]
In [14]:
# (5 points)
from unittest import TestCase
tc = TestCase()
q = Queue(5)
tc.assertEqual(q.data, [None] * 5)
for i in range(5):
q.enqueue(i)
with tc.assertRaises(RuntimeError):
q.enqueue(5)
for i in range(5):
tc.assertEqual(q.dequeue(), i)
tc.assertTrue(q.empty())
In [15]:
# (5 points)
from unittest import TestCase
tc = TestCase()
q = Queue(10)
for i in range(6):
q.enqueue(i)
tc.assertEqual(q.data.count(None), 4)
for i in range(5):
q.dequeue()
tc.assertFalse(q.empty())
tc.assertEqual(q.data.count(None), 9)
tc.assertEqual(q.head, q.tail)
tc.assertEqual(q.head, 5)
for i in range(9):
q.enqueue(i)
with tc.assertRaises(RuntimeError):
q.enqueue(10)
for x, y in zip(q, [5] + list(range(9))):
tc.assertEqual(x, y)
tc.assertEqual(q.dequeue(), 5)
for i in range(9):
tc.assertEqual(q.dequeue(), i)
tc.assertTrue(q.empty())
In [16]:
# (5 points)
from unittest import TestCase
tc = TestCase()
q = Queue(5)
for i in range(5):
q.enqueue(i)
for i in range(4):
q.dequeue()
for i in range(5, 9):
q.enqueue(i)
with tc.assertRaises(RuntimeError):
q.enqueue(10)
q.resize(10)
for x, y in zip(q, range(4, 9)):
tc.assertEqual(x, y)
for i in range(9, 14):
q.enqueue(i)
for i in range(4, 14):
tc.assertEqual(q.dequeue(), i)
tc.assertTrue(q.empty())
tc.assertEqual(q.head, -1)
--------------------------------------------------------------------------- AssertionError Traceback (most recent call last)in () 24 25 for i in range(4, 14): ---> 26 tc.assertEqual(q.dequeue(), i) 27 28 tc.assertTrue(q.empty()) /usr/lib/python3.5/unittest/case.py in assertEqual(self, first, second, msg) 818 """ 819 assertion_func = self._getAssertEqualityFunc(first, second) --> 820 assertion_func(first, second, msg=msg) 821 822 def assertNotEqual(self, first, second, msg=None): /usr/lib/python3.5/unittest/case.py in _baseAssertEqual(self, first, second, msg) 811 standardMsg = '%s != %s' % _common_shorten_repr(first, second) 812 msg = self._formatMessage(msg, standardMsg) --> 813 raise self.failureException(msg) 814 815 def assertEqual(self, first, second, msg=None): AssertionError: 9 != 5
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