USING PYTHON3: Solve def pop(self) for the Stack. class Node(object): \"\"\" A n
ID: 3736228 • Letter: U
Question
USING PYTHON3: Solve def pop(self) for the Stack. class Node(object): """ A node is a simple container with two pieces of information data: the contained information next: a reference to another node We can create node-chains of any size. """ def __init__(self, data, next=None): """ Create a new node for the given data. Pre-conditions: data: Any data value to be stored in the node next: Another node (or None, by default) """ self._data = data self._next = next class Stack(object): def __init__(self): """ Purpose creates an empty queue """ self.__size = 0 # how many elements in the queue self.__first = None # the node chain starts here self.__last = None # the node chain ends here def is_empty(self): """ Purpose checks if the given queue has no data in it Pre-conditions: queue is a queue created by create() Return: True if the queue has no data, or false otherwise """ return self.__size == 0 def size(self): """ Purpose returns the number of data values in the given queue Pre-conditions: queue: a queue created by create() Return: The number of data values in the queue """ return self.__size def push(self, value): """ Purpose adds the given data value to the given queue Pre-conditions: queue: a queue created by create() value: data to be added Post-condition: the value is added to the queue Return: (none) """ n = Node.Node(value) if self.is_empty(): self.__first = n self.__last = n else: n = self.__first n._next = self.__first self.__size += 1 def pop(self): """ Purpose removes and returns a data value from the given queue Post-condition: the first value is removed from the queue Return: the first value in the queue, or None """ TO BE COMPLETE return None
Explanation / Answer
class Node(object):
"""
A node is a simple container with two pieces of information
data: the contained information
next: a reference to another node
We can create node-chains of any size.
"""
def __init__(self, data, next=None):
"""
Create a new node for the given data.
Pre-conditions:
data: Any data value to be stored in the node
next: Another node (or None, by default)
"""
self._data = data
self._next = next
class Stack(object):
def __init__(self):
"""
Purpose
creates an empty queue
"""
self.__size = 0 # how many elements in the queue
self.__first = None # the node chain starts here
self.__last = None # the node chain ends here
def is_empty(self):
"""
Purpose
checks if the given queue has no data in it
Pre-conditions:
queue is a queue created by create()
Return:
True if the queue has no data, or false otherwise
"""
return self.__size == 0
def size(self):
"""
Purpose
returns the number of data values in the given queue
Pre-conditions:
queue: a queue created by create()
Return:
The number of data values in the queue
"""
return self.__size
def push(self, value):
"""
Purpose
adds the given data value to the given queue
Pre-conditions:
queue: a queue created by create()
value: data to be added
Post-condition:
the value is added to the queue
Return:
(none)
"""
n = Node(value)
if self.is_empty():
self.__first = n
self.__last = n
else:
#n = self.__first
n._next = self.__first
self.__first = n
self.__size += 1
def pop(self):
"""
Purpose
removes and returns a data value from the given queue
Post-condition:
the first value is removed from the queue
Return:
the first value in the queue, or None
"""
# if stack is empty
if self.is_empty():
return None
# if stack is not empty
else:
# store the value of first node in temp
temp = self.__first._data
# make second node as the new first
self.__first = self.__first._next
self.__size -= 1
return temp
ob = Stack()
ob.push(1)
ob.push(2)
ob.push(3)
ob.push(4)
while ob.is_empty() == False:
print(ob.pop())
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