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 _apply_layer_operation(example_dict, operation_dict):
    """Applies layer operation to radar data.

    :param example_dict: See doc for `reduce_examples_3d_to_2d`.
    :param operation_dict: See doc for `_check_layer_operation`.
    :return: new_radar_matrix: E-by-M-by-N numpy array resulting from layer
        operation.
    """

    _check_layer_operation(example_dict=example_dict,
                           operation_dict=operation_dict)

    height_diffs_metres = (
        example_dict[RADAR_HEIGHTS_KEY] - operation_dict[MIN_HEIGHT_KEY]
    ).astype(float)
    height_diffs_metres[height_diffs_metres > 0] = -numpy.inf
    min_height_index = numpy.argmax(height_diffs_metres)

    height_diffs_metres = (
        operation_dict[MAX_HEIGHT_KEY] - example_dict[RADAR_HEIGHTS_KEY]
    ).astype(float)
    height_diffs_metres[height_diffs_metres > 0] = -numpy.inf
    max_height_index = numpy.argmax(height_diffs_metres)

    operation_dict[MIN_HEIGHT_KEY] = example_dict[
        RADAR_HEIGHTS_KEY][min_height_index]
    operation_dict[MAX_HEIGHT_KEY] = example_dict[
        RADAR_HEIGHTS_KEY][max_height_index]

    operation_name = operation_dict[OPERATION_NAME_KEY]
    operation_function = OPERATION_NAME_TO_FUNCTION_DICT[operation_name]

    if REFL_IMAGE_MATRIX_KEY in example_dict:
        orig_matrix = example_dict[REFL_IMAGE_MATRIX_KEY][
            ..., min_height_index:(max_height_index + 1), 0]
    else:
        field_index = example_dict[RADAR_FIELDS_KEY].index(
            operation_dict[RADAR_FIELD_KEY])

        orig_matrix = example_dict[RADAR_IMAGE_MATRIX_KEY][
            ..., min_height_index:(max_height_index + 1), field_index]

    return operation_function(orig_matrix, axis=-1), operation_dict