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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 enc_to_clear_filename(fname):
 """ Converts the filename of an encrypted file to cleartext :param fname: :return: filename of clear secret file if found, else None """

    if not fname.lower().endswith('.json'):
        raise CredkeepException('Invalid filetype')

    if not fname.lower().endswith('.enc.json'):
        raise CredkeepException('Not filename of encrypted file')

    clear_fname = fname.replace('.enc.json', '.json')
    print clear_fname

    return clear_fname if exists(clear_fname) else None