def tokenize(self, text):
        '''
        tokenize function in Tokenizer.
        '''
        start = -1
        tokens = []
        for i, character in enumerate(text):
            if character == ' ' or character == '\t':
                if start >= 0:
                    word = text[start:i]
                    tokens.append({
                        'word': word,
                        'original_text': word,
                        'char_begin': start,
                        'char_end': i})
                    start = -1
            else:
                if start < 0:
                    start = i
        if start >= 0:
            tokens.append({
                'word': text[start:len(text)],
                'original_text': text[start:len(text)],
                'char_begin': start,
                'char_end': len(text)
            })
        return tokens
tokenize function in Tokenizer.