def METHOD_NAME(self, name):
    """Load the existing data in the checkpoint file with the given name.
    Or return None if no checkpoint file exists.
    Trying to read an invalid name from an existing checkpoint file will raise an exception.
    """
    if not os.path.isfile(self.file_name):
        self.logger.debug('no checkpoint file yet')
        return None
    self.logger.debug('loading %s',name)
    with h5py.File(self.file_name, 'r') as hdf:
        if name not in hdf:
            self.logger.debug('nothing checkpointed for %s',name)
            return None
        arr = hdf[name][:]
        data_str = arr.tobytes()
        data = pickle.loads(data_str)
        self.logger.info('Loaded checkpointed data for %s.  Size=%d', name, arr.size)
    return data