code: def print_diff(self, summary1=None, summary2=None):
          
          summary.print_(self.diff(summary1=summary1, summary2=summary2))
docs: 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.