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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def export_to_xls(table, filename_or_fobj=None, sheet_name="Sheet1", *args, **kwargs):
 """Export the rows.Table to XLS file and return the saved file."""


    workbook = xlwt.Workbook()
    sheet = workbook.add_sheet(sheet_name)

    prepared_table = prepare_to_export(table, *args, **kwargs)

    field_names = next(prepared_table)
    for column_index, field_name in enumerate(field_names):
        sheet.write(0, column_index, field_name)

    _convert_row = _python_to_xls([table.fields.get(field) for field in field_names])
    for row_index, row in enumerate(prepared_table, start=1):
        for column_index, (value, data) in enumerate(_convert_row(row)):
            sheet.write(row_index, column_index, value, **data)

    return_result = False
    if filename_or_fobj is None:
        filename_or_fobj = BytesIO()
        return_result = True

    source = Source.from_file(filename_or_fobj, mode="wb", plugin_name="xls")
    workbook.save(source.fobj)
    source.fobj.flush()

    if return_result:
        source.fobj.seek(0)
        result = source.fobj.read()
    else:
        result = source.fobj

    if source.should_close:
        source.fobj.close()

    return result