Immutable dictionary, only use as a key for another dictionary

Question

I had the need to implement a hashable dict so I could use a dictionary as a key for another dictionary.

A few months ago I used this implementation: Python hashable

Answer 1

I realize this has already been answered, but types.MappingProxyType is an analogous implementation for Python 3.3. Regarding the original question of safety, there is a discussion in PEP 416 -- Add a frozendict builtin type on why the idea of a frozendict was rejected.