code: def set_parallelism(self, num_instances):
          
          assert (num_instances > 0)
          self.env._set_parallelism(self.src_operator_id, num_instances)
          return self
docs: Sets the number of instances for the source operator of the stream.
  
          Attributes:
               num_instances (int): The level of parallelism for the source
               operator of the stream.