miniredis is a pure Python server that supports a subset of the redis protocol.
The original intent was to have a minimally working (if naïve) PubSub implementation in order to get to grips with the protocol spec, but I eventually realised that a more complete server would be useful for testing and inclusion in some of my projects.
Pure Python performance, dependent on runtime and workload. Your mileage may vary.
I started out by forking coderanger/miniredis for experimentation, and things kind of accreted from there as I started implementing more commands.