code: def eval(self, id1, id2, inst1):
          
          jinst1 = None
          if inst1 is not None:
              jinst1 = inst1.jobject
          return javabridge.call(self.jobject, "eval", "(IILweka/core/Instance;)D", id1, id2, jinst1)
docs: Computes the result of the kernel function for two instances. If id1 == -1, eval use inst1 instead of an
          instance in the dataset.
  
          :param id1: the index of the first instance in the dataset
          :type id1: int
          :param id2: the index of the second instance in the dataset
          :type id2: int
          :param inst1: the instance corresponding to id1 (used if id1 == -1)
          :type inst1: Instance