code: def ranking(self):
      pass
  
file_path: scikit-opt/sko/DE.py
imports: import numpy
  from .base import SkoBase
  from abc import ABCMeta, abstractmethod
  from .operators import crossover, mutation, ranking, selection
  from .GA import GeneticAlgorithmBase, GA
label_desc: Use image node_id 4 for calling the DE obj's underlying member method code with example usage: obj.ranking() without return types