code: def __init__(self, file_store, batch_id):
      self.file_store = file_store
      self.batch_id = batch_id
      self.token = secret_alnum_string(16)
  
      self._data_bytes = bytearray()
      self._offsets_bytes = bytearray()
      self._n_elements = 0
  
imports: import logging
  from typing import Literal, Tuple
  from hailtop.utils import secret_alnum_string
label_desc: Use image node_id 3 to create a new SpecWriter object  with example: obj = SpecWriter(file_store, batch_id)