class_docstr: Python implementation of a format decoder. Override this class and
  add the decoding logic in the :meth:`decode` method.
  
  See :ref:`Writing Your Own File Decoder in Python<file-decoders-py>`
code: def __init__(self, mode, *args):
      self.im = None
      self.state = PyCodecState()
      self.fd = None
      self.mode = mode
      self.init(args)
  
imports: import io
  import itertools
  import struct
  import sys
  from .None import Image
  from ._util import isPath
label_desc: Use image node_id 1 to create a new PyDecoder object  with example: obj = PyDecoder(mode)