There was some interest in getting this to work with ZSH when I first posted it. I just pushed a small change that makes it work for ZSH, and thought people might want to know.
What's the performance impact of starting up a python script every time the shell needs to show the prompt?
On my machine:
real 0m0.075s
user 0m0.047s
sys 0m0.024s
This seems to be a common concern, but I've never noticed a delay in practice.