'Return a string representation of this string. Rounds results to
two decimal places, stripping out any trailing zeroes.
subclassing note: implemented in terms of frac().'

def __str__(self):

    (a, b) = self.frac()
    display = (lambda n: '{:.2f}'.format(n).rstrip('0').rstrip('.'))
    return '{0}/{1}'.format(display(a), display(b))
