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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 _parse_arg(valid_classifications):
 """ Command line parser for coco Parameters valid_classifications: list Available classifications, used for checking input parameters. Returns ------- args : ArgumentParser namespace """


    parser = argparse.ArgumentParser(
        description=('The country converter (coco): a Python package for '
                     'converting country names between '
                     'different classifications schemes. '
                     'Version: {}'.format(__version__)
                     ), prog='coco', usage=('%(prog)s --names --src --to]'))

    parser.add_argument('names',
                        help=('List of countries to convert '
                              '(space separated, country names consisting of '
                              'multiple words must be put in quotation marks).'
                              'Possible classifications: ' +
                              ', '.join(valid_classifications) +
                              '; NB: long, official and short are provided '
                              'as shortcuts for the names classifications'
                              ), nargs='*')
    parser.add_argument('-s', '--src', '--source', '-f', '--from',
                        help=('Classification of the names given, '
                              '(default: inferred from names)'))
    parser.add_argument('-t', '--to',
                        help=('Required classification of the passed names'
                              '(default: "ISO3"'))
    parser.add_argument('-o', '--output_sep',
                        help=('Seperator for output names '
                              '(default: space), e.g. "," '))
    parser.add_argument('-n', '--not_found',
                        default='not found',
                        help=('Fill in value for none found entries. '
                              'If "None" (string), keep the input value '
                              '(default: not found)'))
    parser.add_argument('-a', '--additional_data',
                        help=('Data file with additional country data'
                              '(Same format as the original data file - '
                              'utf-8 encoded tab separated data, same '
                              'column headers as in the general country '
                              'data file; default: not found)'))

    args = parser.parse_args()
    args.src = args.src or None
    args.to = args.to or 'ISO3'
    args.not_found = args.not_found if args.not_found != 'None' else None
    args.output_sep = args.output_sep or ' '

    return args