code: def readline(self):
      maxsize = self._length - self._pos
      self._file.seek(self._offset + self._pos)
      data = self._file.readline()
      if len(data) > maxsize:
          data = data[:maxsize]
      self._pos += len(data)
      return data
  
imports: import errno
  import os
  import sys
  from threading import Lock
  from shutil import copyfileobj
  from whoosh.compat import BytesIO, memoryview_
  from whoosh.filedb.structfile import BufferFile, StructFile
  from whoosh.filedb.filestore import FileStorage, StorageError
  from whoosh.system import emptybytes
  from whoosh.util import random_name
label_desc: Use image node_id 5 for calling the SubFile obj's underlying member method code with example usage: obj.readline() and returns: data