code: def get_default_username(username=None):
      """
      Get default username for Auptimizer
  
      :param username: username
      :return: username
      """
      if username is None:
          if "USER" not in os.environ or not os.environ["USER"]:
              logger.critical("No USER specified, use `default`.")
              return "default"
          else:
              logging.info("Using default user %s" % os.environ["USER"])
              return os.environ["USER"]
      else:
          logging.debug("For user %s" % username)
          return username
  
imports: from __future__ import print_function
  import sys
  import logging
  import os
  from os import path
  from six.moves import input
  from six.moves.configparser import ConfigParser
  import paramiko
  from paramiko import SFTPClient
  from .aup import BasicConfig, print_result
label_desc: Use image node_id 3 for calling a global function with example usage: get_default_username(username) and returns: username, str, os