code: def add(self, key):
      if key not in self.map:
          end = self.end
          curr = end[PREV]
          curr[NEXT] = end[PREV] = self.map[key] = [key, curr, end]
  
file_path: nibabel/nibabel/externals/oset.py
imports: from collections.abc import MutableSet
label_desc: Use image node_id 5 for calling the OrderedSet obj's underlying member method code with example usage: obj.add(key) without return types