code: def test_handler_df(self):
      df = D.features(
          ["sh600519"],
          start_time="20190101",
          end_time="20190201",
          fields=["$close"],
      )
      dh = DataHandlerLP.from_df(df)
      print(dh.fetch())
      self.assertTrue(dh._data.equals(df))
      self.assertTrue(dh._infer is dh._data)
      self.assertTrue(dh._learn is dh._data)
      self.assertTrue(dh.data_loader._data is dh._data)
      fname = "_handler_test.pkl"
      dh.to_pickle(fname, dump_all=True)
  
      with open(fname, "rb") as f:
          dh_d = pickle.load(f)
  
      self.assertTrue(dh_d._data.equals(df))
      self.assertTrue(dh_d._infer is dh_d._data)
      self.assertTrue(dh_d._learn is dh_d._data)
      # Data loader will no longer be useful
      self.assertTrue("_data" not in dh_d.data_loader.__dict__.keys())
      os.remove(fname)
  
file_path: qlib/tests/data_mid_layer_tests/test_handler.py
imports: import os
  import pickle
  import shutil
  import unittest
  from qlib.tests import TestAutoData
  from qlib.data import D
  from qlib.data.dataset.handler import DataHandlerLP
label_desc: Use image node_id 2 for calling the HandlerTests obj's underlying member method code with example usage: obj.test_handler_df() without return types