def get_mask_from_lengths(memory, memory_lengths):
    """Get mask tensor from list of length
    Args:
        memory: (batch, max_time, dim)
        memory_lengths: array like
    """
    mask = memory.data.new(memory.size(0), memory.size(1)).byte().zero_()
    for idx, l in enumerate(memory_lengths):
        mask[idx][:l] = 1
    return ~mask