#an exception to be raised by an empty stack

class Empty(Exception):

    pass

​

class Stack:

    class _Node:

        def __init__(self, e, n):

            self._element = e #Users element

            self._next = n #The next node in the list

​

    def __init__(self):

        self._head = None #Reference the first node in the linked list

        self._size = 0    #The number of elements in the stack

​

    def __len__(self):

        return self._size 

​

    def is_empty(self):

         return len(self) == 0

​

    def push(self, e):

        #add a new element to the stack

        self._head = self._Node(e, self._head)

        self._size += 1

​

    def top(self):

        if self.is_empty():

            raise Empty("Stack is empty.")

        return self._head._element

​

    def pop(self):

        if self.is_empty():

            raise Empty("Stack is empty.")

​

        element = self._head._element

        self._head = self._head._next # make the 

        self._size -= 1

        return element

​

# test the stack

​

S = Stack()

S.push(10)

S.push(20)

S.push(30)

S.push(40)

S.push(50)

print("Size: ", len(S))

​

while not S.is_empty():

    print(S.pop())

#an exception to be raised by an empty stack

class Empty(Exception):

    pass

​

class Stack:

    class _Node:

        def __init__(self, e, n):

            self._element = e #Users element

            self._next = n #The next node in the list

​

    def __init__(self):

        self._head = None #Reference the first node in the linked list

        self._size = 0    #The number of elements in the stack

​

    def __len__(self):

        return self._size 

​

    def is_empty(self):

         return len(self) == 0

​

    def push(self, e):

        #add a new element to the stack

        self._head = self._Node(e, self._head)

        self._size += 1

​

    def top(self):

        if self.is_empty():

            raise Empty("Stack is empty.")

        return self._head._element

​

    def pop(self):

        if self.is_empty():

            raise Empty("Stack is empty.")

​

        element = self._head._element

        self._head = self._head._next # make the 

        self._size -= 1

        return element

​

# test the stack

​

S = Stack()

S.push(10)

S.push(20)

S.push(30)

S.push(40)

S.push(50)

print("Size: ", len(S))

​

while not S.is_empty():

    print(S.pop())