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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 convert_rtf_to_text(filename: str = None, blob: bytes = None, config: TextProcessingConfig = _DEFAULT_CONFIG) -> str: """ Converts RTF to text. """

    unrtf = tools['unrtf']
    if unrtf:  # Best
        args = [unrtf, '--text', '--nopict']
        if UNRTF_SUPPORTS_QUIET:
            args.append('--quiet')
        if filename:
            args.append(filename)
            return get_cmd_output(*args)
        else:
            return get_cmd_output_from_stdin(blob, *args)
    elif pyth:  # Very memory-consuming:
        # https://github.com/brendonh/pyth/blob/master/pyth/plugins/rtf15/reader.py  # noqa
        with get_filelikeobject(filename, blob) as fp:
            doc = pyth.plugins.rtf15.reader.Rtf15Reader.read(fp)
        return (
            pyth.plugins.plaintext.writer.PlaintextWriter.write(doc).getvalue()
        )
    else:
        raise AssertionError("No RTF-reading tool available")