code: def next_target(self):
      self.ref_id = (self.ref_id + 1) % self.length
      return self.ref_list[self.ref_id]
  
imports: import contextlib
  import gzip
  import json
  import re
label_desc: Use image node_id 4 for calling the LoopMMCIF obj's underlying member method code with example usage: obj.next_target() and returns: self