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_example_file(
        top_directory_name, shuffled=True, spc_date_string=None,
        batch_number=None, raise_error_if_missing=True):
    """Looks for file with input examples.

    If `shuffled = True`, this method looks for a file with shuffled examples
    (from many different times).  If `shuffled = False`, this method looks for a
    file with examples from one SPC date.

    :param top_directory_name: Name of top-level directory with input examples.
    :param shuffled: Boolean flag.  The role of this flag is explained in the
        general discussion above.
    :param spc_date_string: [used only if `shuffled = False`]
        SPC date (format "yyyymmdd").
    :param batch_number: [used only if `shuffled = True`]
        Batch number (integer).
    :param raise_error_if_missing: Boolean flag.  If file is missing and
        `raise_error_if_missing = True`, this method will error out.
    :return: example_file_name: Path to file with input examples.  If file is
        missing and `raise_error_if_missing = False`, this is the *expected*
        path.
    :raises: ValueError: if file is missing and `raise_error_if_missing = True`.
    """

    error_checking.assert_is_string(top_directory_name)
    error_checking.assert_is_boolean(shuffled)
    error_checking.assert_is_boolean(raise_error_if_missing)

    if shuffled:
        error_checking.assert_is_integer(batch_number)
        error_checking.assert_is_geq(batch_number, 0)

        first_batch_number = int(number_rounding.floor_to_nearest(
            batch_number, NUM_BATCHES_PER_DIRECTORY))
        last_batch_number = first_batch_number + NUM_BATCHES_PER_DIRECTORY - 1

        example_file_name = (
            '{0:s}/batches{1:07d}-{2:07d}/input_examples_batch{3:07d}.nc'
        ).format(top_directory_name, first_batch_number, last_batch_number,
                 batch_number)
    else:
        time_conversion.spc_date_string_to_unix_sec(spc_date_string)

        example_file_name = (
            '{0:s}/{1:s}/input_examples_{2:s}.nc'
        ).format(top_directory_name, spc_date_string[:4], spc_date_string)

    if raise_error_if_missing and not os.path.isfile(example_file_name):
        error_string = 'Cannot find file.  Expected at: "{0:s}"'.format(
            example_file_name)
        raise ValueError(error_string)

    return example_file_name