def get_nonvaried_cfg_lbls(cfg_list, default_cfg=None, mainkey='_cfgname'):
    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']
    """
    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
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']