code: def _random_binary_string_matrix(rows, cols, max_length):
      """Returns a list of lists of random strings"""
      return [
          [_random_binary_string_gen(max_length) for _ in range(cols)]
          for _ in range(rows)
      ]
  
imports: from __future__ import division
  import random
  from collections import OrderedDict
  from decimal import Decimal
  from functools import partial
  import numpy
  import pytz
  from pyspark import Row
  from pyspark.sql import SparkSession
  from pyspark.sql.types import StringType, DecimalType, DoubleType, StructField, IntegerType, StructType, DateType, TimestampType, ShortType, ArrayType
  from petastorm.codecs import CompressedImageCodec, NdarrayCodec, ScalarCodec
  from petastorm.etl.dataset_metadata import materialize_dataset
  from petastorm.etl.rowgroup_indexers import SingleFieldIndexer
  from petastorm.etl.rowgroup_indexing import build_rowgroup_index
  from petastorm.unischema import Unischema, UnischemaField, dict_to_spark_row
label_desc: Use image node_id 2 for calling a global function with example usage: _random_binary_string_matrix(rows, cols, max_length) and returns: unknown