def to_file(self, destination, format='csv', csv_delimiter=',', csv_header=True):
    """Save the results to a local file in CSV format.

    Args:
      destination: path on the local filesystem for the saved results.
      format: the format to use for the exported data; currently only 'csv' is supported.
      csv_delimiter: for CSV exports, the field delimiter to use. Defaults to ','
      csv_header: for CSV exports, whether to include an initial header line. Default true.
    Raises:
      An Exception if the operation failed.
    """
    f = codecs.open(destination, 'w', 'utf-8')
    fieldnames = []
    for column in self.schema:
      fieldnames.append(column.name)
    if sys.version_info[0] == 2:
      csv_delimiter = csv_delimiter.encode('unicode_escape')
    writer = csv.DictWriter(f, fieldnames=fieldnames, delimiter=csv_delimiter)
    if csv_header:
      writer.writeheader()
    for row in self:
      writer.writerow(row)
    f.close()