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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 default_filename_decoder():
 """ Creates a decoder which parses CWR filenames following the old or the new convention. :return: a CWR filename decoder for the old and the new conventions """

    factory = default_filename_grammar_factory()

    grammar_old = factory.get_rule('filename_old')
    grammar_new = factory.get_rule('filename_new')

    return FileNameDecoder(grammar_old, grammar_new)