code: def cc(self):
          
          _years = range(self._start, self._end+1)
          try:
              return list(zip(_years, [d.get('$') for d in self._citeInfoMatrix['cc']]))
          except AttributeError:  # No citations
              return list(zip(_years, [0]*len(_years)))
docs: List of tuples of yearly number of citations
          for specified years.