class_docstr: Fetch training curve data from CloudWatch Metrics for a specific training job.
code: def _fetch_dataframe(self):
      for metric_name in self._metric_names:
          self._fetch_metric(metric_name)
      return pd.DataFrame(self._data)
  
imports: from __future__ import print_function, absolute_import
  from abc import ABCMeta, abstractmethod
  from collections import defaultdict, OrderedDict
  import datetime
  import logging
  from six import with_metaclass
  from sagemaker.session import Session
  from sagemaker.utils import DeferredError
  from sagemaker.lineage import artifact
label_desc: Use image node_id 6 for calling the TrainingJobAnalytics obj's underlying member method code with example usage: obj._fetch_dataframe() and returns: pd