code: def send(src, dst, nfeat, efeat, message_func):
      """Send message from src to dst."""
      src_feat = op.RowReader(nfeat, src)
      dst_feat = op.RowReader(nfeat, dst)
      msg = message_func(src_feat, dst_feat, efeat)
      return msg
  
imports: import warnings
  import numpy
  import paddle.fluid
  import paddle.fluid.layers
  from pgl.utils import op
  from pgl.utils import paddle_helper
  from pgl.utils.logger import log
label_desc: Use image node_id 1 for calling a global function with example usage: send(src, dst, nfeat, efeat, message_func) and returns: msg