def secure_filename(filename):
    r"""Borrowed from :mod:`werkzeug.utils`, under the BSD 3-clause license.

    Pass it a filename and it will return a secure version of it.  This
    filename can then safely be stored on a regular file system and passed
    to :func:`os.path.join`.  The filename returned is an ASCII only string
    for maximum portability.

    On windows systems the function also makes sure that the file is not
    named after one of the special device files.

    >>> secure_filename("My cool movie.mov")
    'My_cool_movie.mov'
    >>> secure_filename("../../../etc/passwd")
    'etc_passwd'
    >>> secure_filename(u'i contain cool \xfcml\xe4uts.txt')
    'i_contain_cool_umlauts.txt'

    The function might return an empty filename.  It's your responsibility
    to ensure that the filename is unique and that you generate random
    filename if the function returned an empty one.

    :param filename: the filename to secure
    """
    _filename_ascii_strip_re = re.compile(r'[^A-Za-z0-9_.-]')
    _windows_device_files = ('CON', 'AUX', 'COM1', 'COM2', 'COM3', 'COM4',
                             'LPT1', 'LPT2', 'LPT3', 'PRN', 'NUL')
    if isinstance(filename, text_type):
        from unicodedata import normalize
        filename = normalize('NFKD', filename).encode('ascii', 'ignore')
        if not PY2:
            filename = filename.decode('ascii')
    for sep in os.path.sep, os.path.altsep:
        if sep:
            filename = filename.replace(sep, ' ')
    filename = str(_filename_ascii_strip_re.sub('', '_'.join(
                   filename.split()))).strip('._')

    # on nt a couple of special files are present in each folder.  We
    # have to ensure that the target file is not such a filename.  In
    # this case we prepend an underline
    if os.name == 'nt' and filename and \
       filename.split('.')[0].upper() in _windows_device_files:
        filename = '_' + filename

    return filename
def _restore_checkpoint(self,
                          master,
                          saver=None,
                          checkpoint_dir=None,
                          checkpoint_filename_with_path=None,
                          wait_for_checkpoint=False,
                          max_wait_secs=7200,
                          config=None):
    """Creates a `Session`, and tries to restore a checkpoint.


    Args:
      master: `String` representation of the TensorFlow master to use.
      saver: A `Saver` object used to restore a model.
      checkpoint_dir: Path to the checkpoint files. The latest checkpoint in the
        dir will be used to restore.
      checkpoint_filename_with_path: Full file name path to the checkpoint file.
      wait_for_checkpoint: Whether to wait for checkpoint to become available.
      max_wait_secs: Maximum time to wait for checkpoints to become available.
      config: Optional `ConfigProto` proto used to configure the session.

    Returns:
      A pair (sess, is_restored) where 'is_restored' is `True` if
      the session could be restored, `False` otherwise.

    Raises:
      ValueError: If both checkpoint_dir and checkpoint_filename_with_path are
        set.
    """
    self._target = master

    # This is required to so that we initialize the TPU device before
    # restoring from checkpoint since we'll be placing variables on the device
    # and TPUInitialize wipes out the memory of the device.
    strategy = distribution_strategy_context.get_strategy()
    if strategy and hasattr(strategy.extended,
                            "_experimental_initialize_system"):
      strategy.extended._experimental_initialize_system()  # pylint: disable=protected-access

    sess = session.Session(self._target, graph=self._graph, config=config)
    if checkpoint_dir and checkpoint_filename_with_path:
      raise ValueError("Can not provide both checkpoint_dir and "
                       "checkpoint_filename_with_path.")
    # If either saver or checkpoint_* is not specified, cannot restore. Just
    # return.
    if not saver or not (checkpoint_dir or checkpoint_filename_with_path):
      return sess, False

    if checkpoint_filename_with_path:
      _restore_checkpoint_and_maybe_run_saved_model_initializers(
          sess, saver, checkpoint_filename_with_path)
      return sess, True

    # Waits up until max_wait_secs for checkpoint to become available.
    wait_time = 0
    ckpt = checkpoint_management.get_checkpoint_state(checkpoint_dir)
    while not ckpt or not ckpt.model_checkpoint_path:
      if wait_for_checkpoint and wait_time < max_wait_secs:
        logging.info("Waiting for checkpoint to be available.")
        time.sleep(self._recovery_wait_secs)
        wait_time += self._recovery_wait_secs
        ckpt = checkpoint_management.get_checkpoint_state(checkpoint_dir)
      else:
        return sess, False

    # Loads the checkpoint.
    _restore_checkpoint_and_maybe_run_saved_model_initializers(
        sess, saver, ckpt.model_checkpoint_path)
    saver.recover_last_checkpoints(ckpt.all_model_checkpoint_paths)
    return sess, True