stack.py

"""
stack.py
author: James heliotis
description: A linked stack (LIFO) implementation
"""

from node import LinkedNode

class Stack:

    __slots__ = "top"

    def __init__( self ):
        """ Create a new empty stack.
        """
        self.top = None

    def __str__( self ):
        """ Return a string representation of the contents of
            this stack, top value first.
        """
        result = "Stack["
        n = self.top
        while n != None:
            result += " " + str( n.value )
            n = n.link
        result += " ]"
        return result

    def is_empty( self ):
        return self.top == None

    def push( self, newValue ):
        self.top = LinkedNode( newValue, self.top )

    def pop( self ):
        assert not self.is_empty(), "Pop from empty stack"
        self.top = self.top.link

    def peek( self ):
        assert not self.is_empty(), "peek on empty stack"
        return self.top.value

    insert = push
    remove = pop

def test():
    s = Stack()
    print( s )
    for value in 1, 2, 3:
        s.push( value )
        print( s )
    print( "Popping:", s.peek() )
    s.pop()
    print( s )
    for value in 15, 16:
        s.insert( value )
        print( s )
    print( "Removing:", s.peek() )
    s.remove()
    print( s )
    while not s.is_empty():
        print( "Popping:", s.peek() )
        s.pop()
        print( s )
    print( "Trying one too many pops... ", end="" )
    try:
        s.pop()
        print( "Problem: it succeeded!" )
    except Exception as e:
        print( "Exception was '" + str( e ) + "'" )


if __name__ == "__main__":
    test()