class_docstr: Predictor for multitask models.
  
  Registered as a `Predictor` with name "multitask".
  
  This predictor is tightly coupled to `MultiTaskDatasetReader` and `MultiTaskModel`, and will not work if
  used with other readers or models.
code: def predict_batch_instance(
      self, instances: List[Instance]
  ) -> List[JsonDict]:
      task_to_instances: Dict[
          str, List[Instance]
      ] = collections.defaultdict(lambda: [])
      for instance in instances:
          task_field = instance["task"]
          if not isinstance(task_field, MetadataField):
              raise ValueError(self._WRONG_FIELD_ERROR)
          task: str = task_field.metadata
          if not isinstance(
              self._dataset_reader, MultiTaskDatasetReader
          ):
              raise ConfigurationError(self._WRONG_READER_ERROR)
          self._dataset_reader.readers[task].apply_token_indexers(
              instance
          )
          task_to_instances[task].append(instance)
  
      outputs = []
      for task, instances in task_to_instances.items():
          outputs.extend(super().predict_batch_instance(instances))
  
      return outputs
  
file_path: allennlp/allennlp/predictors/multitask.py
imports: import collections
  from typing import Type, List, Dict
  from allennlp.common import JsonDict
  from allennlp.data import Instance
  from allennlp.models.multitask import MultiTaskModel
  from allennlp.predictors.predictor import Predictor
  from allennlp.common.util import sanitize
  from allennlp.data.fields import MetadataField
  from allennlp.common.checks import ConfigurationError
  from allennlp.data.dataset_readers import MultiTaskDatasetReader
label_desc: Use image node_id 4 for calling the MultiTaskPredictor obj's underlying member method code with example usage: obj.predict_batch_instance(instances) and returns: outputs