def download_file(url, dest=None, chunk_size=1024, replace="ask",
                  label="Downloading {dest_basename} ({size:.2f}MB)",
                  expected_extension=None):
    """Download a file from a given URL and display progress.

    :param dest: If the destination exists and is a directory, the filename
        will be guessed from the Content-Disposition header. If the destination
        is an existing file, the user will either be prompted to overwrite, or
        the file will be replaced (depending on the value of **replace**). If
        the destination does not exist, it will be used as the filename.
    :param int chunk_size: bytes read in at a time.
    :param replace: If `False`, an existing destination file will not be
        overwritten.
    :param label: a string which is formatted and displayed as the progress bar
        label. Variables provided include *dest_basename*, *dest*, and *size*.
    :param expected_extension: if set, the filename will be sanitized to ensure
        it has the given extension. The extension should not start with a dot
        (`.`).
    """
    dest = Path(dest or url.split("/")[-1])
    response = get(url, stream=True)
    if (dest.exists()
            and dest.is_dir()
            and "Content-Disposition" in response.headers):
        content_disposition = rfc6266.parse_requests_response(response)
        if expected_extension is not None:
            filename = content_disposition.filename_sanitized(
                expected_extension)
        filename = secure_filename(filename)
        dest = dest / filename
    if dest.exists() and not dest.is_dir():
        if (replace is False
                or replace == "ask"
                and not click.confirm("Replace {}?".format(dest))):
            return str(dest)
    size = int(response.headers.get("content-length", 0))
    label = label.format(dest=dest, dest_basename=dest.name,
                         size=size/1024.0/1024)
    with click.open_file(str(dest), "wb") as f:
        content_iter = response.iter_content(chunk_size=chunk_size)
        with click.progressbar(content_iter, length=size/1024,
                               label=label) as bar:
            for chunk in bar:
                if chunk:
                    f.write(chunk)
                    f.flush()
    return str(dest)
def find_storm_images_3d(
        top_directory_name, radar_source, radar_field_names,
        radar_heights_m_agl, first_spc_date_string, last_spc_date_string):
    """Locates files with 3-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: See doc for `find_storm_images_2d`.
    :param radar_source: Same.
    :param radar_field_names: List (length F_r) of radar fields.  Each item must
        be accepted by `radar_utils.check_field_name`.
    :param radar_heights_m_agl: numpy array (length H_r) of radar heights
        (metres above ground level).
    :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.
    :return: radar_file_name_matrix: numpy array (D x F_r x H_r) 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:
        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:
        file_dict = storm_images.find_many_files_myrorss_or_mrms(
            top_directory_name=top_directory_name, radar_source=radar_source,
            radar_field_names=[radar_utils.REFL_NAME],
            reflectivity_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, raise_error_if_any_missing=False)

    radar_file_name_matrix = 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:
        radar_file_name_matrix = numpy.reshape(
            radar_file_name_matrix,
            (num_file_times, 1, len(radar_heights_m_agl))
        )

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