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 init(cls, eltype, data, kdims, vdims):
        import cudf
        import pandas as pd

        element_params = eltype.param.objects()
        kdim_param = element_params['kdims']
        vdim_param = element_params['vdims']

        if isinstance(data, (cudf.Series, pd.Series)):
            data = data.to_frame()

        if not isinstance(data, cudf.DataFrame):
            data, _, _ = PandasInterface.init(eltype, data, kdims, vdims)
            data = cudf.from_pandas(data)

        columns = list(data.columns)
        ncols = len(columns)
        index_names = [data.index.name]
        if index_names == [None]:
            index_names = ['index']
        if eltype._auto_indexable_1d and ncols == 1 and kdims is None:
            kdims = list(index_names)

        if isinstance(kdim_param.bounds[1], int):
            ndim = min([kdim_param.bounds[1], len(kdim_param.default)])
        else:
            ndim = None
        nvdim = vdim_param.bounds[1] if isinstance(vdim_param.bounds[1], int) else None
        if kdims and vdims is None:
            vdims = [c for c in columns if c not in kdims]
        elif vdims and kdims is None:
            kdims = [c for c in columns if c not in vdims][:ndim]
        elif kdims is None:
            kdims = list(columns[:ndim])
            if vdims is None:
                vdims = [d for d in columns[ndim:((ndim+nvdim) if nvdim else None)]
                         if d not in kdims]
        elif kdims == [] and vdims is None:
            vdims = list(columns[:nvdim if nvdim else None])

        # Handle reset of index if kdims reference index by name
        for kd in kdims:
            kd = dimension_name(kd)
            if kd in columns:
                continue
            if any(kd == ('index' if name is None else name)
                   for name in index_names):
                data = data.reset_index()
                break
        if any(isinstance(d, (np.int64, int)) for d in kdims+vdims):
            raise DataError("cudf DataFrame column names used as dimensions "
                            "must be strings not integers.", cls)

        if kdims:
            kdim = dimension_name(kdims[0])
            if eltype._auto_indexable_1d and ncols == 1 and kdim not in columns:
                data = data.copy()
                data.insert(0, kdim, np.arange(len(data)))

        for d in kdims+vdims:
            d = dimension_name(d)
            if len([c for c in columns if c == d]) > 1:
                raise DataError('Dimensions may not reference duplicated DataFrame '
                                'columns (found duplicate %r columns). If you want to plot '
                                'a column against itself simply declare two dimensions '
                                'with the same name. '% d, cls)
        return data, {'kdims':kdims, 'vdims':vdims}, {}