'Return a unique file name.'

def _get_filename(self):

    if (self._fname is None):
        timestamp = datetime.datetime.now().strftime('%Y%m%d-%H%M%S')
        fname = ('%s-%s.log' % (timestamp, abs(id(self))))
        self._fname = os.path.join(self.file_path, fname)
    return self._fname
