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 subset_examples(example_dict, indices_to_keep, create_new_dict=False):
    """Subsets examples in dictionary.

    :param example_dict: See doc for `write_example_file`.
    :param indices_to_keep: 1-D numpy array with indices of examples to keep.
    :param create_new_dict: Boolean flag.  If True, this method will create a
        new dictionary, leaving the input dictionary untouched.
    :return: example_dict: Same as input, but possibly with fewer examples.
    """

    error_checking.assert_is_integer_numpy_array(indices_to_keep)
    error_checking.assert_is_numpy_array(indices_to_keep, num_dimensions=1)
    error_checking.assert_is_boolean(create_new_dict)

    if not create_new_dict:
        for this_key in MAIN_KEYS:
            optional_key_missing = (
                this_key not in REQUIRED_MAIN_KEYS
                and this_key not in example_dict
            )

            if optional_key_missing:
                continue

            if this_key == TARGET_MATRIX_KEY:
                if this_key in example_dict:
                    example_dict[this_key] = (
                        example_dict[this_key][indices_to_keep, ...]
                    )
                else:
                    example_dict[TARGET_VALUES_KEY] = (
                        example_dict[TARGET_VALUES_KEY][indices_to_keep]
                    )

                continue

            if this_key == FULL_IDS_KEY:
                example_dict[this_key] = [
                    example_dict[this_key][k] for k in indices_to_keep
                ]
            else:
                example_dict[this_key] = example_dict[this_key][
                    indices_to_keep, ...]

        return example_dict

    new_example_dict = {}

    for this_key in METADATA_KEYS:
        sounding_key_missing = (
            this_key in [SOUNDING_FIELDS_KEY, SOUNDING_HEIGHTS_KEY]
            and this_key not in example_dict
        )

        if sounding_key_missing:
            continue

        if this_key == TARGET_NAMES_KEY:
            if this_key in example_dict:
                new_example_dict[this_key] = example_dict[this_key]
            else:
                new_example_dict[TARGET_NAME_KEY] = example_dict[
                    TARGET_NAME_KEY]

            continue

        new_example_dict[this_key] = example_dict[this_key]

    for this_key in MAIN_KEYS:
        optional_key_missing = (
            this_key not in REQUIRED_MAIN_KEYS
            and this_key not in example_dict
        )

        if optional_key_missing:
            continue

        if this_key == TARGET_MATRIX_KEY:
            if this_key in example_dict:
                new_example_dict[this_key] = (
                    example_dict[this_key][indices_to_keep, ...]
                )
            else:
                new_example_dict[TARGET_VALUES_KEY] = (
                    example_dict[TARGET_VALUES_KEY][indices_to_keep]
                )

            continue

        if this_key == FULL_IDS_KEY:
            new_example_dict[this_key] = [
                example_dict[this_key][k] for k in indices_to_keep
            ]
        else:
            new_example_dict[this_key] = example_dict[this_key][
                indices_to_keep, ...]

    return new_example_dict