docs: def return_features(self, names='all'):
          """
          Returns a list of extracted features from the database
  
          Parameters
          ----------
          names : list of strings, a list of feature names which are to be retrieved from the database, if equal
          to 'all', the all features will be returned, default value: 'all'
  
          Returns
          -------
          A list of lists, each 'inside list' corresponds to a single data point, each element of the 'inside list' is a
          feature (can be of any type)
          """
          if self._prepopulated is False:
              raise errors.EmptyDatabase(self.dbpath)
          else:
              return return_features_base(self.dbpath, self._set_object, names)