code: def write_mnist(image_file, label_file, output_path, **kwargs):
      images = _extract_mnist_images(image_filepath=image_file)
      labels = _extract_mnist_labels(labels_filepath=label_file)
      _write_ndarrays(images, labels, output_path, **kwargs)
  
imports: from pyspark import SparkContext
  from pyspark.sql import SparkSession
  from zoo import init_nncontext
  from zoo.orca.data import SparkXShards
  from zoo.orca.data.file import open_text, write_text
  from zoo.orca.data.image.utils import chunks, dict_to_row, row_to_dict, encode_schema, decode_schema, SchemaField, FeatureType, DType, ndarray_dtype_to_dtype, decode_feature_type_ndarray, pa_fs
  from zoo.orca.data.image.voc_dataset import VOCDatasets
  from bigdl.util.common import get_node_and_core_number
  import os
  import numpy
  import random
  import pyarrow.parquet
  import io
  import math
label_desc: Use image node_id 6 for calling a global function with example usage: write_mnist(image_file, label_file, output_path) without return types