code: def lookup_user(args):
      
      user = args.user
      if user is None:
          user = gitusername()
  
      if user is None:
          raise RuntimeError(textwrap.dedent("""\
              unable to determine a git user name
              Specify --user option\
          """))
  
      debug("user name is {user}".format(user=user))
  
      return user
docs: Return the user name to use when creating git objects or exit
      program.
  
      Parameters
      ----------
      args: parser.parse_args()
  
      Returns
      -------
      user: `string`
          git user name