class_docstr: A multi-tower multi-GPU predictor.
  It builds one predictor for each tower.
code: def _do_call(self, dp):
      # use the first tower for compatible PredictorBase interface
      return self.predictors[0]._do_call(dp)
  
file_path: tensorpack/tensorpack/predict/multigpu.py
imports: import tensorflow
  from ..input_source import PlaceholderInput
  from ..tfutils.tower import PredictTowerContext
  from ..utils import logger
  from .base import OnlinePredictor
label_desc: Use image node_id 2 for calling the MultiTowerOfflinePredictor obj's underlying member method code with example usage: obj._do_call(dp) and returns: self