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 find_storm_images_2d(
        top_directory_name, radar_source, radar_field_names,
        first_spc_date_string, last_spc_date_string, radar_heights_m_agl=None,
        reflectivity_heights_m_agl=None):
    """Locates files with 2-D storm-centered radar images.

    D = number of SPC dates in time period (`first_spc_date_string`...
        `last_spc_date_string`)

    :param top_directory_name: Name of top-level directory.  Files therein will
        be found by `storm_images.find_storm_image_file`.
    :param radar_source: Data source (must be accepted by
        `radar_utils.check_data_source`).
    :param radar_field_names: 1-D list of radar fields.  Each item must be
        accepted by `radar_utils.check_field_name`.
    :param first_spc_date_string: First SPC date (format "yyyymmdd").  This
        method will locate files from `first_spc_date_string`...
        `last_spc_date_string`.
    :param last_spc_date_string: Same.
    :param radar_heights_m_agl: [used only if radar_source = "gridrad"]
        1-D numpy array of radar heights (metres above ground level).  These
        heights apply to all radar fields.
    :param reflectivity_heights_m_agl: [used only if radar_source != "gridrad"]
        1-D numpy array of reflectivity heights (metres above ground level).
        These heights do not apply to other radar fields.
    :return: radar_file_name_matrix: D-by-C numpy array of file paths.
    """

    radar_utils.check_data_source(radar_source)
    first_spc_date_unix_sec = time_conversion.spc_date_string_to_unix_sec(
        first_spc_date_string)
    last_spc_date_unix_sec = time_conversion.spc_date_string_to_unix_sec(
        last_spc_date_string)

    if radar_source == radar_utils.GRIDRAD_SOURCE_ID:
        storm_image_file_dict = storm_images.find_many_files_gridrad(
            top_directory_name=top_directory_name,
            radar_field_names=radar_field_names,
            radar_heights_m_agl=radar_heights_m_agl,
            start_time_unix_sec=first_spc_date_unix_sec,
            end_time_unix_sec=last_spc_date_unix_sec,
            one_file_per_time_step=False, raise_error_if_all_missing=True)
    else:
        storm_image_file_dict = storm_images.find_many_files_myrorss_or_mrms(
            top_directory_name=top_directory_name, radar_source=radar_source,
            radar_field_names=radar_field_names,
            reflectivity_heights_m_agl=reflectivity_heights_m_agl,
            start_time_unix_sec=first_spc_date_unix_sec,
            end_time_unix_sec=last_spc_date_unix_sec,
            one_file_per_time_step=False,
            raise_error_if_all_missing=True, raise_error_if_any_missing=False)

    radar_file_name_matrix = storm_image_file_dict[
        storm_images.IMAGE_FILE_NAMES_KEY]
    num_file_times = radar_file_name_matrix.shape[0]

    if radar_source == radar_utils.GRIDRAD_SOURCE_ID:
        num_field_height_pairs = (
            radar_file_name_matrix.shape[1] * radar_file_name_matrix.shape[2]
        )
        radar_file_name_matrix = numpy.reshape(
            radar_file_name_matrix, (num_file_times, num_field_height_pairs)
        )

    time_missing_indices = numpy.unique(
        numpy.where(radar_file_name_matrix == '')[0]
    )
    return numpy.delete(
        radar_file_name_matrix, time_missing_indices, axis=0)