class Stack:
def __init__(self):
self.size = 0
self.storage = LinkedList()
def __len__(self):
return self.size
def push(self, value):
self.storage.add_to_tail(value)
self.size += 1
def pop(self):
if self.size > 0:
value = self.storage.tail.get_value()
self.storage.remove_tail()
self.size -= 1
return value
else:
return None
