Preserves only samples which satisfy the following inequality:
            min_len <= src sample sequence length <= max_len AND
            min_len <= tgt sample sequence length <= max_len

        :param min_len: minimum sequence length
        :param max_len: maximum sequence length

def filter_raw_data(self, min_len, max_len):
        """
        Preserves only samples which satisfy the following inequality:
            min_len <= src sample sequence length <= max_len AND
            min_len <= tgt sample sequence length <= max_len

        :param min_len: minimum sequence length
        :param max_len: maximum sequence length
        """
        initial_len = len(self.raw_src)
        filtered_src = []
        filtered_tgt = []
        filtered_src_len = []
        filtered_tgt_len = []
        for src, tgt in zip(self.raw_src, self.raw_tgt):
            src_len = src.count(' ') + 1
            tgt_len = tgt.count(' ') + 1
            if min_len <= src_len <= max_len and \
                    min_len <= tgt_len <= max_len:
                filtered_src.append(src)
                filtered_tgt.append(tgt)
                filtered_src_len.append(src_len)
                filtered_tgt_len.append(tgt_len)

        self.raw_src = filtered_src
        self.raw_tgt = filtered_tgt
        self.src_len = filtered_src_len
        self.tgt_len = filtered_tgt_len
        filtered_len = len(self.raw_src)
        logging.info(f'Pairs before: {initial_len}, after: {filtered_len}')