def xlsx_to_tsv(file_object, f='web'):
    """
    Converts xlsx SBtab file to tsv format.

    Parameters
    ----------
    file_object: xlsx file object
        SBtab table as xlsx file object.
    f: str
        String indicating how the file object is represented ('web' for online file handling, otherwise normal file handling)
    
    Returns: str
        SBtab table as tsv string.
    """
    import openpyxl
    from io import BytesIO
    if f == 'web':
        wb = openpyxl.load_workbook(filename=BytesIO(file_object))
    else:
        wb = openpyxl.load_workbook(filename=file_object)
    ws = wb.active
    ranges = wb[ws.title]
    table_string = ''
    for row in ranges:
        for column in row:
            if str(row[0].value).startswith('!'):
                if column.value != None and str(column.value) != '':
                    table_string += str(column.value) + '\t'
            else:
                table_string += str(column.value) + '\t'
        table_string = table_string[:-1] + '\n'
    return table_string
