class Stack(object):
def __init__(self):
self.S = SinglyLinkedList()
def is_empty(self):
return self.S.is_empty()
def push(self, element):
self.S.insert(SinglyLinkedListNode(element)) # Linked list implementation of stack overflow do not exist
def pop(self):
head_node = self.S.delete_head()
if head_node:
return head_node.key
else:
raise IndexError('stack underflow')
