'Initializes the Caption.
Args:
sentence: List of word ids in the caption.
state: Model state after generating the previous word.
logprob: Log-probability of the caption.
score: Score of the caption.
metadata: Optional metadata associated with the partial sentence. If not
None, a list of strings with the same length as \'sentence\'.'

def __init__(self, sentence, state, logprob, score, metadata=None):

    self.sentence = sentence
    self.state = state
    self.logprob = logprob
    self.score = score
    self.metadata = metadata
