code: def eval(self, i):
      return i - 1
  
imports: import datetime
  import os
  import unittest
  import uuid
  import pytz
  from pyflink.common import Row
  from pyflink.table import DataTypes, expressions
  from pyflink.table.expressions import call
  from pyflink.table.udf import ScalarFunction, udf, FunctionContext
  from pyflink.testing import source_sink_utils
  from pyflink.testing.test_case_utils import PyFlinkStreamTableTestCase, PyFlinkBatchTableTestCase
label_desc: Use image node_id 1 for calling the SubtractOne obj's underlying member method code with example usage: obj.eval(i) and returns: unknown