vocab_build.py

import nltk
import pickle
import argparse
from collections import Counter
import json

class Vocabulary(object):
    """Simple vocabulary wrapper."""
    def __init__(self):
        #need two dictionaries for easy access of words and indices
        self.word2idx = {}
        self.idx2word = {}
        self.idx = 0

    def add_word(self, word):
        #if that particular word is not present then add and update id
        if not word in self.word2idx:
            self.word2idx[word] = self.idx
            self.idx2word[self.idx] = word
            self.idx += 1

    #Constructor
    def __call__(self, word):
        if not word in self.word2idx:
            return self.word2idx['<unk>']
        return self.word2idx[word]

    def __len__(self):
        return len(self.word2idx)

    def print_vocab(self):
        print(self.idx2word)

def build_vocab(json_file, threshold):
    file = open(json_file, "r")
    data = json.loads(file.read())
    counter = Counter()
    #There are two ids in the keys, images and dataset. Dataset is just a string
    for i, id in enumerate(data.keys()):
        for j in range(0, len(data['images'])):
            name = data['images'][j]['filename'].split('_')[0]
            sentence = data['images'][j]['sentences'][0]['raw']
            tokens = nltk.tokenize.word_tokenize(sentence)
            counter.update(tokens)

    print("[{}/{}] Tokenized the captions.".format(i+1, len(data.keys())))
    
    # If the word frequency is less than 'threshold', then the word is discarded.
    words = [word for word, cnt in counter.items() if cnt >= threshold]
    words = [word.lower() for i, word in enumerate(words) if word.isalpha()]

    # Create a vocab wrapper and add some special tokens.
    vocab = Vocabulary()
    vocab.add_word('<pad>')
    vocab.add_word('<start>')
    vocab.add_word('<end>')
    vocab.add_word('<unk>')

    # Add the words to the vocabulary.
    for i, word in enumerate(words):
        vocab.add_word(word)
    vocab.print_vocab()
    return vocab

def main(args):
    vocab = build_vocab(json_file=args.caption_path, threshold=args.threshold)
    vocab_path = args.vocab_path
    with open(vocab_path, 'wb') as f:
        pickle.dump(vocab, f)
    print("Total vocabulary size: {}".format(len(vocab)))
    print("Saved the vocabulary wrapper to '{}'".format(vocab_path))


if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument('--caption_path', type=str, 
                        default="", 
                        help='path for train annotation file')
    parser.add_argument('--vocab_path', type=str, default='', 
                        help='path for saving vocabulary wrapper')
    parser.add_argument('--threshold', type=int, default=1, 
                        help='minimum word count threshold')
    args = parser.parse_args()
    main(args)