    def print_diff(self, summary1=None, summary2=None):
        """Compute diff between to summaries and print it.

        If no summary is provided, the diff from the last to the current
        summary is used. If summary1 is provided the diff from summary1
        to the current summary is used. If summary1 and summary2 are
        provided, the diff between these two is used.
        """
        summary.print_(self.diff(summary1=summary1, summary2=summary2))