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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 prepare_xml(args, parser):
 """Prepares XML files for stripping. This process creates a single, normalised TEI XML file for each work. """

    if args.source == constants.TEI_SOURCE_CBETA_GITHUB:
        corpus_class = tacl.TEICorpusCBETAGitHub
    else:
        raise Exception('Unsupported TEI source option provided')
    corpus = corpus_class(args.input, args.output)
    corpus.tidy()