code: def make_mapper(features):
      
      if not features:
          features = Feature(input=[], transformer=NullTransformer())
      if not iterable(features):
          features = (features, )
      return DataFrameMapper(
          [t.as_input_transformer_tuple() for t in features],
          input_df=True)
docs: Make a DataFrameMapper from a feature or list of features
  
      Args:
          features (Union[Feature, List[Feature]]): feature or list of features
  
      Returns:
          DataFrameMapper: mapper made from features