#===============================================================================

# implementation of a stack using linked list. i.e stack size is dynamic

#===============================================================================

class Node:

def __init__(self,key, value):

self.key = key

self.value = value

self.next = None

def __str__(self):

return "[(%d, %s)]" %(self.key, self.value)

class Stack:

def __init__(self):

self.head = None

self.tail = None

def __str__(self):

l = []

print "___________________________________"

print "Top of the stack = %s" % (self.head)

current = self.head

if not current:

return "[]"

while(current):

l.append("%s" % (current, ))

current = current.next

return " --> ".join(l)

def push(self, key, value):

node = Node(key, value)

if (self.head is None):

self.head = node

self.tail = node

print "PUSH : element pushed to the stack, key: %s | value: %s" %(key, value)

else:

head = self.head

self.head = node

self.head.next = head

print "PUSH : element pushed to the stack, key: %s | value: %s" %(key, value)

def pop(self):

if self.head is None:

print "Stack is already empty"

else:

print "POP: element deleted from top of the stack, key: %s | value: %s" %(self.head.key, self.head.value)

self.head = self.head.next

def peek(self):

if self.head is None:

print "Stack is already empty"

else:

print "PEEK: key: %s | value: %s is on top of the stack" %(self.head.key, self.head.value)

def main():

new_stack = Stack()

new_stack.push(1, "hello")

new_stack.push(2, "world")

new_stack.push(5, "test")

new_stack.push(7, "test2")

new_stack.pop()

new_stack.peek()

print new_stack

if __name__ == '__main__':

main()