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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 _attempt_to_raise_license_error(data_dir):
 """Raise an error if NLPIR has detected a missing or expired license. :param str data_dir: The directory containing NLPIR's `Data` directory. :raises LicenseError: The NLPIR license appears to be missing or expired. """

    if isinstance(data_dir, bytes):
        data_dir = _decode(data_dir)
    data_dir = os.path.join(data_dir, 'Data')

    current_date = dt.date.today().strftime('%Y%m%d')
    timestamp = dt.datetime.today().strftime('[%Y-%m-%d %H:%M:%S]')
    data_files = os.listdir(data_dir)

    for f in data_files:
        if f == (current_date + '.err'):
            file_name = os.path.join(data_dir, f)
            with fopen(file_name) as error_file:
                for line in error_file:
                    if not line.startswith(timestamp):
                        continue
                    if 'Not valid license' in line:
                        raise LicenseError('Your license appears to have '
                                           'expired. Try running "pynlpir '
                                           'update".')
                    elif 'Can not open License file' in line:
                        raise LicenseError('Your license appears to be '
                                           'missing. Try running "pynlpir '
                                           'update".')