def show_approx(self, numfmt='%.3g'):
        """Show the probabilities rounded and sorted by key, for the
        sake of portable doctests."""
        return ', '.join([('%s: ' + numfmt) % (v, p)
                          for (v, p) in sorted(self.prob.items())])
Show the probabilities rounded and sorted by key, for the
        sake of portable doctests.