code: def get_nonvaried_cfg_lbls(cfg_list, default_cfg=None, mainkey='_cfgname'):
      r
      try:
          cfgname_list = [cfg[mainkey] for cfg in cfg_list]
      except KeyError:
          cfgname_list = [''] * len(cfg_list)
      nonvaried_cfg = partition_varied_cfg_list(cfg_list, default_cfg)[0]
      cfglbl_list = [get_cfg_lbl(nonvaried_cfg, name) for name in cfgname_list]
      return cfglbl_list
docs: r"""
      TODO: this might only need to return a single value. Maybe not if the names
          are different.
  
      Args:
          cfg_list (list):
          default_cfg (None): (default = None)
  
      Returns:
          list: cfglbl_list
  
      CommandLine:
          python -m utool.util_gridsearch --exec-get_nonvaried_cfg_lbls
  
      Example:
          >>> # ENABLE_DOCTEST
          >>> from utool.util_gridsearch import *  # NOQA
          >>> import utool as ut
          >>> cfg_list = [{'_cfgname': 'test', 'f': 1, 'b': 1},
          >>>             {'_cfgname': 'test', 'f': 2, 'b': 1},
          >>>             {'_cfgname': 'test', 'f': 3, 'b': 1, 'z': 4}]
          >>> default_cfg = None
          >>> cfglbl_list = get_nonvaried_cfg_lbls(cfg_list, default_cfg)
          >>> result = ('cfglbl_list = %s' % (ut.repr2(cfglbl_list),))
          >>> print(result)
          cfglbl_list = ['test:b=1', 'test:b=1', 'test:b=1']