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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 generate_prepare_subparser(subparsers):
 """Adds a sub-command parser to `subparsers` to prepare source XML files for stripping."""

    parser = subparsers.add_parser(
        'prepare', description=constants.PREPARE_DESCRIPTION,
        epilog=constants.PREPARE_EPILOG, formatter_class=ParagraphFormatter,
        help=constants.PREPARE_HELP)
    parser.set_defaults(func=prepare_xml)
    utils.add_common_arguments(parser)
    parser.add_argument('-s', '--source', dest='source',
                        choices=constants.TEI_SOURCE_CHOICES,
                        default=constants.TEI_SOURCE_CBETA_GITHUB,
                        help=constants.PREPARE_SOURCE_HELP,
                        metavar='SOURCE')
    parser.add_argument('input', help=constants.PREPARE_INPUT_HELP,
                        metavar='INPUT')
    parser.add_argument('output', help=constants.PREPARE_OUTPUT_HELP,
                        metavar='OUTPUT')