code: def save_data(cls, fname="data.csv"):
      # Utility to get data into another package.
      df = pd.DataFrame(index=np.arange(len(cls.weights)))
      df["weights"] = cls.weights
      if cls.data.ndim == 1:
          df["data1"] = cls.data
      else:
          for k in range(cls.data.shape[1]):
              df["data%d" % (k + 1)] = cls.data[:, k]
      df.to_csv(fname)
  
imports: import numpy
  from scipy import stats
  import pandas
  from numpy.testing import assert_, assert_almost_equal, assert_allclose
  from statsmodels.stats.weightstats import DescrStatsW, CompareMeans, ttest_ind, ztest, zconfint
  from statsmodels.tools.testing import Holder
label_desc: Use image node_id 2 for calling the CheckExternalMixin obj's underlying member method code with example usage: obj.save_data(cls, fname) without return types