def METHOD_NAME(source_block, target_block):
    """
    Returns a 2-dimensional (2-D) attention mask
    :param source_block: 1-D array
    :param target_block: 1-D array
    """
    mask = (target_block[None, :] >= 1) * (source_block[:, None] >= 1)
    mask = mask.astype(np.int64)
    # (source_length, target_length)
    return mask