[Python Stack]

stack.py

# Using lists as stacks
stack = [3, 4, 5]
stack.append(6) ## Same as push
stack.pop()

## Custom implementation of stack using LinkedList (See LinkedList)
class Element(object):
    def __init__(self, value):
        self.value = value
        self.next = None
        
class LinkedList(object):
    def __init__(self, head=None):
        self.head = head
        
    def append(self, new_element):
        current = self.head
        if self.head:
            while current.next:
                current = current.next
            current.next = new_element
        else:
            self.head = new_element

    def insert_first(self, new_element):
        "Insert new element as the head of the LinkedList"
        new_element.next = self.head
        self.head = new_element
	
    def delete_first(self):
      "Delete the first (head) element in the LinkedList as return it"
      deleted = self.head
      if self.head:
          self.head = self.head.next
          deleted.next = None
      return deleted

class Stack(object):
    def __init__(self,top=None):
        self.ll = LinkedList(top)

    def push(self, new_element):
        "Push (add) a new element onto the top of the stack"
        self.ll.insert_first(new_element)

    def pop(self):
        "Pop (remove) the first element off the top of the stack and return it"
        return self.ll.delete_first()