def get_filenames(i):
    """Returns the filepaths for the output MusicXML and .png files.
   
    Parameters:
    - i: unique identifier for the score

    Returns:
    - (sheet_png_filepath, musicxml_out_filepath)
    """

    output_folder_prefix = "dataset/"
    sheet_png_out_filepath = output_folder_prefix + "{}-sheet.png".format(i)
    musicxml_out_filepath = output_folder_prefix + "{}-musicxml.xml".format(i)

    return (sheet_png_out_filepath, musicxml_out_filepath)