class_docstr: Dict-like object to hold immutable latent state.
  
  This must either be given a name when constructed::
  
      latent = named.Dict("root")
  
  or must be immediately stored in a ``named.Object``::
  
      latent = named.Object("root")
      latent.xs = named.Dict()  # Must be bound to a Object before use.
  
  .. warning:: This data structure is write-once: data may be added but may
      not be mutated or removed. Trying to mutate this data structure may
      result in silent errors.
code: def __getitem__(self, key):
      try:
          return super().__getitem__(key)
      except KeyError as e:
          if self._name is None:
              raise RuntimeError(
                  "Cannot access an unnamed named.Dict"
              ) from e
          value = Object("{}[{!r}]".format(self._name, key))
          super(Object, value).__setattr__(
              "_set_value", lambda value: self.__setitem__(key, value)
          )
          super().__setitem__(key, value)
          return value
  
imports: import functools
  import pyro
label_desc: Use image node_id 4 for calling the Dict obj's underlying member method code with example usage: obj.__getitem__(key) and returns: super, value