class_docstr: Generic hierarchical cache for transformed functions.
  
  The keys are soft references (i.e. they are discarded when the key is
  destroyed) created from the source function by `_get_key`. The subkeys are
  strong references and can be any value. Typically they identify different
  kinds of transformation.
code: def __getitem__(self, entity):
      key = self._get_key(entity)
      parent = self._cache.get(key, None)
      if parent is None:
          # The bucket is initialized to support this usage:
          #   cache[key][subkey] = value
          self._cache[key] = parent = {}
      return parent
  
file_path: DALI/dali/python/nvidia/dali/_autograph/pyct/cache.py
imports: import inspect
  import weakref
label_desc: Use image node_id 4 for calling the _TransformedFnCache obj's underlying member method code with example usage: obj.__getitem__(entity) and returns: parent