class_docstr: list of beams at specific time-step
docstr: return best beams, specify the max. number of beams to be returned (beam width)
docstr_tok: ["return","best","beams",",","specify","the","max",".","number","of","beams","to","be","returned","(","beam","width",")"]
code: def getBestBeams(self, num):
      "return best beams, specify the max. number of beams to be returned (beam width)"
      u = [v for (_, v) in self.beams.items()]
      lmWeight = 1
      return sorted(
          u,
          reverse=True,
          key=lambda x: x.getPrTotal() * (x.getPrTextual() ** lmWeight),
      )[:num]
  
imports: from __future__ import division
  from __future__ import print_function
  import copy
label_desc: Use image node_id 3 for calling the BeamList obj's underlying member method code with example usage: obj.getBestBeams(num) and returns: sorted