class_docstr: Cache for inversion operator. 
code: def __missing__(self, filter):
      result = _Invert(filter)
      self[filter] = result
      return result
  
imports: from __future__ import unicode_literals
  from abc import ABCMeta, abstractmethod
  from six import with_metaclass
  from prompt_toolkit.utils import test_callable_args
label_desc: Use image node_id 1 for calling the _InvertCache obj's underlying member method code with example usage: obj.__missing__(filter) and returns: result