code: def _opref_to_string(opref):
      pkg_type = util.shlex_quote(opref.pkg_type)
      pkg_name = util.shlex_quote(opref.pkg_name)
      pkg_version = util.shlex_quote(opref.pkg_version)
      model_name = util.shlex_quote(opref.model_name)
      op_name = util.shlex_quote(opref.op_name)
      return (
          f"{pkg_type}:{pkg_name} {pkg_version} {model_name} {op_name}"
      )
  
file_path: guildai/guild/opref.py
imports: import collections
  import logging
  import os
  import re
  from guild import util
label_desc: Use image node_id 8 for calling a global function with example usage: _opref_to_string(opref) and returns: pkg_type, str, pkg_name, str, pkg_version, str, model_name, str, op_name