class_docstr: Work around for Python 2, for which pickle fails on instance method.
code: def __call__(self, *args, **kwargs):
      return self.func.call_and_shelve(*args, **kwargs)
  
file_path: nilearn/nilearn/_utils/cache_mixin.py
imports: import os
  import warnings
  from joblib import Memory
  import nilearn
  from .helpers import stringify_path
label_desc: Use image node_id 2 for calling the _ShelvedFunc obj's underlying member method code with example usage: obj.__call__() and returns: self