def _get_feature_names(self, key, var, agg):
    _agg = []
    for a in agg:
        if (not isinstance(a, str)):
            _agg.append(a.__name__)
        else:
            _agg.append(a)
    return ['_'.join(([a, v, 'groupby'] + key)) for v in var for a in _agg]
def _get_feature_names(self, key, var, agg):
    _agg = []
    for a in agg:
        if (not isinstance(a, str)):
            _agg.append(a.__name__)
        else:
            _agg.append(a)
    return ['_'.join(([a, v, 'groupby'] + key)) for v in var for a in _agg]