liststack.py

# Implementation of the Stack ADT using a Python list.
class Stack:
    # Creates an empty stack
    def __init__( self ):
        self._theItems = list()

    # Returns True if the stack is empty or False otherwise.
    def isEmpty( self ):
        return len( self ) == 0

    # Returns the number of items in the stack.
    def __len__( self ):
        return len( self._theItems )

    # Returns the top item on the stack without removing it.
    def peek( self ):
        assert not self.isEmpty(), "Cannot peek at an empty stack"
        return self._theItems[-1]

    # Removes and returns the top item on the stack
    def pop( self ):
        assert not self.isEmpty(), "Cannot pop from an empty stack"
        return self._theItems.pop()

    # Push an item onto the top of  the stack.
    def push( self, item ):
        self._theItems.append( item )