>      # Let's write reusable code, and unit test it.
>      def add_money(amounts):
>          # do arithmetic in pennies so as not to
> accumulate float errors
>          pennies = sum([round(int(amount * 100)) for
> amount in amounts])
>          return float(pennies / 100.0)
>      import unittest
>      class TestAddMoney(unittest.TestCase):
>          def test_float_errors(self):
>              self.failUnlessEqual(add_money([0.13,
> 0.02]), 0.15)
>              self.failUnlessEqual(add_money([100.01,
> 99.99]), 200)
>              self.failUnlessEqual(add_money([0,
> -13.00, 13.00]), 0)
>      if __name__ == '__main__':
>          unittest.main()

> I believe I've still kept it to 13 lines.