Allows the user to download a graph's data as a CSV file.
    :return: show a dialog box that allows the user to download the CSV file.

def get_graph_csv():
    """
    Allows the user to download a graph's data as a CSV file.
    :return: show a dialog box that allows the user to download the CSV file.
    """
    assert request.method == "POST", "POST request expected received {}".format(request.method)
    if request.method == "POST":
        try:
            selected_variable_table = request.form["selected_variable_table"]
            filename = utils.generate_graph_csv(selected_variable_table)
            return send_file(filename, as_attachment=True, attachment_filename='{}.csv'.format(selected_variable_table))
        except Exception as e:
            logging.error(e)
    return jsonify({"0": "__EMPTY"})