A reader ran into an issue with the latest release of pyuvm (not the 2.8.0 release) in which the example and the README file contained what appears to be an extraneous .class_ attribute when extending tests.
This was an intentional modification to pyuvm to make it work more smoothly with cocotb 1.7. It would have allowed the user to use the @pyuvm test decorator and the TESTCASE command line option.
Unfortunately, updating the @pyuvm decorator to work with the cocotb regression manager would have meant changing the code in the example repository and the book. So I backed the change out.
That means that the pyuvm repository has a new HEAD on master, so if you pulled from the master branch, you should do a pull to get the corrected code.