feed_var {
    name: "words"
    is_lod_tensor: true
    feed_type: 0
    shape: -1
}
feed_var {
    name: "label"
    is_lod_tensor: false
    feed_type: 0
    shape: 1    
}
fetch_var {
    name: "cost"
    shape: 1
}
fetch_var {
    name: "acc"
    shape: 1
}
fetch_var {
    name: "prediction"
    shape: 2
}