:param str prefix: Prefix to add/remove from keys. :param collections.MutableMapping mapping: Dict-like object to wrap :param bool fancy_repr: If True, show fancy repr, otherwise just show dict's :param bool dictify_repr: If True, cast mapping to a dict on repr
(self, prefix, mapping, only_prefixed=True, fancy_repr=True, dictify_repr=False)
source not stored for this graph (policy: none)