class_docstr: An abstract class represening StreamDataset which has unknown length.
  Generally, all unknown length datasets should subclass it.
  All subclasses should overwrite :code:`__iter__`.
  
  Examples:
      .. code-block:: python
  
          from pgl.utils.data import StreamDataset
  
          class MyStreamDataset(StreamDataset):
              def __init__(self):
                  self.data = list(range(0, 40))
                  self.count = 0
  
              def __iter__(self):
                   for data in self.dataset:
                      self.count += 1
                      if self.count % self._worker_info.num_workers != self._worker_info.fid:
                          continue
                      # do something (like parse data)  of your data
                      time.sleep(0.1)
                      yield data
code: def __iter__(self):
      raise NotImplementedError
  
imports: import os
  import sys
  import numpy
  import json
  import io
  from subprocess import Popen, PIPE
label_desc: Use image node_id 1 for calling the StreamDataset obj's underlying member method code with example usage: obj.__iter__() without return types