code: def _push_stream(self, idx):
      if self._push_streams[idx] is None:
          self._push_streams[idx] = cuda.Stream()
      return self._push_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 2 for calling the StreamPool obj's underlying member method code with example usage: obj._push_stream(idx) and returns: self