Print statistics to csv file

def output_to_csv(sources, csv_writeable_file):
    """Print statistics to csv file"""
    file_exists = os.path.isfile(csv_writeable_file)

    with open(csv_writeable_file, 'a') as csvfile:
        csv_dict = OrderedDict()
        csv_dict.update({'Time': time.strftime("%Y-%m-%d_%H:%M:%S")})
        summaries = [val for key, val in sources.items()]
        for summarie in summaries:
            csv_dict.update(summarie.source.get_sensors_summary())

        fieldnames = [key for key, val in csv_dict.items()]
        writer = csv.DictWriter(csvfile, fieldnames=fieldnames)

        if not file_exists:
            writer.writeheader()  # file doesn't exist yet, write a header
        writer.writerow(csv_dict)