look ma' no ifs!

gistfile1.txt

#!/usr/bin/env python

import unittest
import sys

class EmptyStackElement(object):

    def pop(self):
        raise StopIteration


class StackElement(object):

    def __init__(self, element, previous):
        self.element = element
        self.previous = previous

    def pop(self):
        return self.element

class Stack(object):

    def __init__(self):
        self.top_element = EmptyStackElement()

    def pop(self):
        poped = self.top_element.pop()
        self.top_element = self.top_element.previous
        return poped

    def push(self, element):
        self.top_element = StackElement(element, self.top_element)


class StackTestCases(unittest.TestCase):

    def test_empty(self):
        s = Stack()

        try:
            s.pop()
            self.fail('No exception raised')
        except StopIteration:
            pass
        else:
            self.fail('Wrong exception')

    def test_push(self):
        s = Stack()
        self.assertEqual(s.push(42), None)

    def test_push_pop(self):
        s = Stack()
        s.push(42)
        self.assertEqual(s.pop(), 42)
        try:
            s.pop()
            self.fail('No exception raised')
        except StopIteration:
            pass
        else:
            self.fail('Wrong exception')

            

if __name__ == '__main__':
    sys.exit(unittest.main())