nodelist.py

from collections import namedtuple

Node = namedtuple('Node', 'value next')

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

    def push(self, value):
        n = Node(value, self.top)
        self.top = n

    def pop(self):
        if not self.top:
            return None
        try:
            return self.top.value
        finally:
            self.top = self.top.next

    def itervalues(self):
        top = self.top
        while top:
            yield top.value
            top = top.next

    def values(self):
        return list(self.itervalues())


if __name__ == '__main__':
    stack = Stack()

    assert stack.pop() == None
    stack.push('foo')
    assert stack.pop() == 'foo'
    assert stack.pop() == None
    stack.push('bar')
    stack.push('baz')
    stack.push('foobar')
    assert stack.values() == ['foobar', 'baz', 'bar']
    assert stack.pop() == 'foobar'
    assert stack.pop() == 'baz'
    assert stack.pop() == 'bar'