code: def convert_stack(node, **kwargs):
      """Map MXNet's stack operator to onnx operators."""
      name, input_nodes, attrs = get_inputs(node, kwargs)
      axis = int(attrs.get("axis", 0))
      create_tensor([axis], name + "_axis", kwargs["initializer"])
      idx = 0
      nodes = []
      for input_node in input_nodes:
          nodes.append(
              onnx.helper.make_node(
                  "Unsqueeze",
                  inputs=[input_node, name + "_axis"],
                  outputs=[name + "_unsqueeze" + str(idx)],
              )
          )
          idx += 1
  
      nodes.append(
          onnx.helper.make_node(
              "Concat",
              inputs=[
                  name + "_unsqueeze" + str(i)
                  for i in range(len(nodes))
              ],
              outputs=[name],
              name=name,
              axis=axis,
          )
      )
      return nodes
  
imports: import re
  import logging
  import numpy
  from .._export_onnx import MXNetGraph
label_desc: Use image node_id 18 for calling a global function with example usage: convert_stack(node) and returns: nodes