code: def _pull_stream(self, idx):
      if self._pull_streams[idx] is None:
          self._pull_streams[idx] = cuda.Stream()
      return self._pull_streams[idx]
  
imports: import numpy
  import paddle
  from paddle.framework import core
  from paddle.device import cuda
  from pgl.utils.logger import log
label_desc: Use image node_id 3 for calling the StreamPool obj's underlying member method code with example usage: obj._pull_stream(idx) and returns: self