code: def data():
      true = results_kalman_filter.uc_uni
      data_ = pd.DataFrame(
          true["data"],
          index=pd.date_range("1947-01-01", "1995-07-01", freq="QS"),
          columns=["GDP"],
      )
      data_["lgdp"] = np.log(data_["GDP"])
      return data_
  
file_path: statsmodels/statsmodels/tsa/statespace/tests/test_pickle.py
imports: import pickle
  import numpy
  import pandas
  from numpy.testing import assert_equal, assert_allclose
  import pytest
  from statsmodels.tsa.statespace import sarimax
  from statsmodels.tsa.statespace.kalman_filter import KalmanFilter
  from statsmodels.tsa.statespace.representation import Representation
  from statsmodels.tsa.statespace.structural import UnobservedComponents
  from .results import results_kalman_filter
label_desc: Use image node_id 1 for calling a global function with example usage: data() and returns: data_