code: def load_dframe(self, dframe):
          
          filename_series = dframe[self.key]
          loaded_data = filename_series.map(self.filetype.data)
          keys = [list(el.keys()) for el in loaded_data.values]
          for key in set().union(*keys):
              key_exists = key in dframe.columns
              if key_exists:
                  self.warning("Appending '_data' suffix to data key %r to avoid"
                               "overwriting existing metadata with the same name." % key)
              suffix = '_data' if key_exists else ''
              dframe[key+suffix] = loaded_data.map(lambda x: x.get(key, np.nan))
          return dframe
docs: Load the file contents into the supplied dataframe using the
          specified key and filetype.