code: def store(self, seq_id, seq):
          
  
          if not self._writeable:
              raise RuntimeError("Cannot write -- opened read-only")
  
          # open a file for writing if necessary
          # path: <root_dir>/<reldir>/<basename>
          #                  <---- relpath ---->
          #       <------ dir_ ----->
          #       <----------- path ----------->
          if self._writing is None:
              reldir = datetime.datetime.utcnow().strftime("%Y/%m%d/%H%M")
              basename = str(time.time()) + ".fa.bgz"
              relpath = os.path.join(reldir, basename)
  
              dir_ = os.path.join(self._root_dir, reldir)
              path = os.path.join(self._root_dir, reldir, basename)
              makedirs(dir_, exist_ok=True)
              fabgz = FabgzWriter(path)
              self._writing = {"relpath": relpath, "fabgz": fabgz}
              logger.info("Opened for writing: " + path)
  
          self._writing["fabgz"].store(seq_id, seq)
          alpha = "".join(sorted(set(seq)))
          self._db.execute("""insert into seqinfo (seq_id, len, alpha, relpath)
                           values (?, ?, ?,?)""", (seq_id, len(seq), alpha, self._writing["relpath"]))
          return seq_id
docs: store a sequence with key seq_id.  The sequence itself is stored in
          a fasta file and a reference to it in the sqlite3 database.