Obtain a list of image paths corresponding to training or eval case.

  Args:
    tmp_dir: str, the root path to which raw images were written, at the
      top level having meta/ and raw/ subdirs.
    case: bool, whether obtaining file paths for training (true) or eval
      (false).
    training_fraction: float, the fraction of the sub-image path list to
      consider as the basis for training examples.

  Returns:
    list: A list of file paths.

  Raises:
    ValueError: if images not found in tmp_dir, or if training_fraction would
      leave no examples for eval.

def _get_case_file_paths(tmp_dir, case, training_fraction=0.95):
  """Obtain a list of image paths corresponding to training or eval case.

  Args:
    tmp_dir: str, the root path to which raw images were written, at the
      top level having meta/ and raw/ subdirs.
    case: bool, whether obtaining file paths for training (true) or eval
      (false).
    training_fraction: float, the fraction of the sub-image path list to
      consider as the basis for training examples.

  Returns:
    list: A list of file paths.

  Raises:
    ValueError: if images not found in tmp_dir, or if training_fraction would
      leave no examples for eval.
  """

  paths = tf.gfile.Glob("%s/*.jpg" % tmp_dir)

  if not paths:
    raise ValueError("Search of tmp_dir (%s) " % tmp_dir,
                     "for subimage paths yielded an empty list, ",
                     "can't proceed with returning training/eval split.")

  split_index = int(math.floor(len(paths)*training_fraction))

  if split_index >= len(paths):
    raise ValueError("For a path list of size %s "
                     "and a training_fraction of %s "
                     "the resulting split_index of the paths list, "
                     "%s, would leave no elements for the eval "
                     "condition." % (len(paths),
                                     training_fraction,
                                     split_index))

  if case:
    return paths[:split_index]
  else:
    return paths[split_index:]