code: def save_past_metrics(
      self,
      data_past: TimeSeriesDataFrame,
      target: str = "target",
      **kwargs,
  ) -> None:
      self._past_target_mean = 1.0 + data_past[target].abs().mean()
  
file_path: autogluon/timeseries/tests/unittests/common.py
imports: import random
  from typing import Dict, List, Optional, Union
  import numpy
  import pandas
  from gluonts.dataset.common import ListDataset
  from autogluon.timeseries.dataset import TimeSeriesDataFrame
  from autogluon.timeseries.dataset.ts_dataframe import ITEMID, TIMESTAMP
  from autogluon.timeseries.metrics import TimeSeriesScorer
label_desc: Use image node_id 1 for calling the CustomMetric obj's underlying member method code with example usage: obj.save_past_metrics(data_past, target) without return types