To add to the previous answer, the notebooks on the v3 version tag are frozen (like v3 development) and you should generally read the updated notebooks from https://docs.pymc.io/projects/examples/en/latest/
In this case, the blackbox external likelihood I think hasn’t been updated, but we have added an alternative version that uses numpy instead of cython to implement the black box function:
- Using a “black box” likelihood function (Cython) — PyMC documentation
- Using a “black box” likelihood function (numpy) — PyMC documentation
We are already updating the notebooks to use the beta release of pymc v4, and you might want a frozen version of the notebooks where all still use v3. You will see a version menu at the bottom right of the page, you can select the snapshot from this January in that menu for this.