code: def read(self, size=None):
      if size is None:
          size = self._length - self._pos
      else:
          size = min(size, self._length - self._pos)
      if size < 0:
          size = 0
  
      if size > 0:
          self._file.seek(self._offset + self._pos)
          self._pos += size
          return self._file.read(size)
      else:
          return emptybytes
  
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 4 for calling the SubFile obj's underlying member method code with example usage: obj.read(size) and returns: self, emptybytes