class_docstr: Abstract parent class for all Bert Ranker agents.
code: def __init__(self, opt, shared=None):
      raise RuntimeError(
          "You must specify which ranker to use. Choices: \n"
          "-m bert_ranker/bi_encoder_ranker \n"
          "-m bert_ranker/cross_encoder_ranker \n"
          "-m bert_ranker/both_encoder_ranker"
      )
  
imports: from .bi_encoder_ranker import BiEncoderRankerAgent
  from .cross_encoder_ranker import CrossEncoderRankerAgent
  from .both_encoder_ranker import BothEncoderRankerAgent
  from parlai.core.torch_agent import TorchAgent
label_desc: Use image node_id 1 to create a new BertRankerAgent object from inherited base classes: TorchAgent with example: obj = BertRankerAgent(opt, shared)