code: def begin(self):
      if self._output_dir:
          self._summary_writer = SummaryWriterCache.get(
              self._output_dir
          )
  
      self._next_step = None
      self._global_step = tf.train.get_global_step()
      if self._global_step is None:
          raise RuntimeError(
              "Global step must be created for VarVisHook."
          )
  
file_path: luminoth/luminoth/utils/hooks/var_vis_hook.py
imports: import tensorflow
  from tensorflow.python.training.summary_io import SummaryWriterCache
label_desc: Use image node_id 2 for calling the VarVisHook obj's underlying member method code with example usage: obj.begin() without return types