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 _compare_metadata(netcdf_dataset, example_dict):
    """Compares metadata between existing NetCDF file and new batch of examples.

    This method contains a large number of `assert` statements.  If any of the
    `assert` statements fails, this method will error out.

    :param netcdf_dataset: Instance of `netCDF4.Dataset`.
    :param example_dict: See doc for `write_examples_with_3d_radar`.
    :raises: ValueError: if the two sets have different metadata.
    """

    include_soundings = SOUNDING_MATRIX_KEY in example_dict

    orig_example_dict = {
        TARGET_NAMES_KEY: [
            str(s) for s in
            netCDF4.chartostring(netcdf_dataset.variables[TARGET_NAMES_KEY][:])
        ],
        ROTATED_GRIDS_KEY: bool(getattr(netcdf_dataset, ROTATED_GRIDS_KEY)),
        RADAR_FIELDS_KEY: [
            str(s) for s in netCDF4.chartostring(
                netcdf_dataset.variables[RADAR_FIELDS_KEY][:])
        ],
        RADAR_HEIGHTS_KEY: numpy.array(
            netcdf_dataset.variables[RADAR_HEIGHTS_KEY][:], dtype=int
        )
    }

    if example_dict[ROTATED_GRIDS_KEY]:
        orig_example_dict[ROTATED_GRID_SPACING_KEY] = int(
            getattr(netcdf_dataset, ROTATED_GRID_SPACING_KEY)
        )

    if include_soundings:
        orig_example_dict[SOUNDING_FIELDS_KEY] = [
            str(s) for s in netCDF4.chartostring(
                netcdf_dataset.variables[SOUNDING_FIELDS_KEY][:])
        ]
        orig_example_dict[SOUNDING_HEIGHTS_KEY] = numpy.array(
            netcdf_dataset.variables[SOUNDING_HEIGHTS_KEY][:], dtype=int
        )

    for this_key in orig_example_dict:
        if isinstance(example_dict[this_key], numpy.ndarray):
            if numpy.array_equal(example_dict[this_key],
                                 orig_example_dict[this_key]):
                continue
        else:
            if example_dict[this_key] == orig_example_dict[this_key]:
                continue

        error_string = (
            '\n"{0:s}" in existing NetCDF file:\n{1:s}\n\n"{0:s}" in new batch '
            'of examples:\n{2:s}\n\n'
        ).format(
            this_key, str(orig_example_dict[this_key]),
            str(example_dict[this_key])
        )

        raise ValueError(error_string)