class_docstr: This class handles iteration events to log summaries to
  the TensorBoard log.
docstr: Decide whether to save a TensorBoard log entry for a given iteration.
  
  :param c_iter: Integer of the current iteration number
  :return: boolean True if is writing at the current iteration
code: def _is_writing(self, c_iter):
      """
      Decide whether to save a TensorBoard log entry for a given iteration.
  
      :param c_iter: Integer of the current iteration number
      :return: boolean True if is writing at the current iteration
      """
      if self.writer_valid is None or self.writer_train is None:
          return False
      if not self.summary_dir:
          return False
      return c_iter % self.tensorboard_every_n == 0
  
file_path: NiftyNet/niftynet/engine/handler_tensorboard.py
imports: import os
  import tensorflow
  from niftynet.engine.application_variables import TF_SUMMARIES
  from niftynet.engine.signal import TRAIN, VALID, ITER_STARTED, ITER_FINISHED, GRAPH_CREATED
  from niftynet.io.misc_io import get_latest_subfolder
label_desc: Use image node_id 5 for calling the TensorBoardLogger obj's underlying member method code with example usage: obj._is_writing(c_iter) and returns: unknown, False, False