code: def top_cited(papers, topn=20, verbose=False):
      
  
      if verbose:
          print "Finding top "+unicode(topn)+" most cited papers..."
  
      counts = citation_count(papers, verbose=verbose)
  
      if type(topn) is int:
          n = topn
      elif type(topn) is float:
          n = int(np.around(topn*len(counts), decimals=-1))
      top = dict(sorted(counts.items(),
                         key=operator.itemgetter(1),
                         reverse=True)[:n]).keys()
  
      return top, counts
docs: Generates a list of the topn (or topn%) most cited papers.
  
      Parameters
      ----------
      papers : list
          A list of :class:`.Paper` instances.
      topn : int or float {0.-1.}
          Number (int) or percentage (float) of top-cited papers to return.
      verbose : bool
          If True, prints status messages.
  
      Returns
      -------
      top : list
          A list of 'ayjid' keys for the topn most cited papers.
      counts : dict
          Citation counts for all papers cited by papers.