code: def _check_nano_envs():
      for k in envs_checklist:
          if not os.environ.get(k, None):
              _unset_envs.append(k)
  
      if len(_unset_envs):
          highlight_boundary = "\n{}\n".format("*" * 150)
          warning(
              f"{highlight_boundary}Nano environment variables {_unset_envs} are not set.\n"
              f"Please run `source bigdl-nano-init` to initialize them, "
              f"or you can prefix `bigdl-nano-init` to the command you run.\n"
              f"\nExample:\n"
              f"bigdl-nano-init python pytorch-lenet.py --device ipex"
              f"{highlight_boundary}"
          )
  
imports: import os
  from logging import warning
  import atexit
  from bigdl.nano.utils.common import output_suggestions
label_desc: Use image node_id 1 for calling a global function with example usage: _check_nano_envs() without return types