Ladon (example has syntax error)

Question

(Ladon) I use the command 'serve' and get a syntax error pointing to the 'serve' keyword, I've also tried substituting the 'serve' with 'testserve' because the -ctl script has notes talking about the name change but using 'testserve' also gives the same error. I've ladon-3.3-ctl.py and my test script is based on the Ladon's example (script name: Calculator.py). Can you suggest a trouble-shooting direction? Thanks.