class_docstr: Base class for stub image loaders.
  
  A stub loader is an image loader that can identify files of a
  certain format, but relies on external code to load the file.
code: def _open(self):
      raise NotImplementedError(
          "StubImageFile subclass must implement _open"
      )
  
imports: import io
  import itertools
  import struct
  import sys
  from .None import Image
  from ._util import isPath
label_desc: Use image node_id 1 for calling the StubImageFile obj's underlying member method code with example usage: obj._open() without return types