docs: def _data(self, copy=False):
          """
          Get data kwargs of the container (i.e. dataframe and series objects).
          """
          data = {}
          for key, obj in vars(self).items():
              if isinstance(obj, (pd.Series, pd.DataFrame, pd.SparseSeries, pd.SparseDataFrame)):
                  if copy:
                      data[key] = obj.copy(deep=True)
                  else:
                      data[key] = obj
          return data