code: def open(self, function_context):
      self.counter_sum = 0
  
imports: import unittest
  from pyflink.table import DataTypes
  from pyflink.table.udf import TableFunction, udtf, ScalarFunction, udf
  from pyflink.table.expressions import col
  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 MultiEmit obj's underlying member method code with example usage: obj.open(function_context) without return types