I don't think SM buys all the 3rd party add-on Python scripts and tests them. Certainly I didn't. :)

So there's no answer born of experience and actual evidence for the entire body of work that exists. We can only guess.

There is a new version of the core Python interpreter, so there may be small differences having nothing to do with Poser 8, and everything to do with the new version of Python. But, by and large, Python is Python, until you get to Python 3.0. Then most everything breaks. Poser 8 is not using Python 3.0.

There can be changes to the libraries, as for example the Tk changes that broke face_off's scripts. These usually are minor changes to get them to work.

Semidieu and PhilC should really be able to answer this better than I. I haven't yet done any Python scripting specifically in P8. I can tell you that VSS and Matmatic are working as is, no changes. However, my Parmatic utility is very unhappy, waking up far too often, and Paser is bringing the computer to its knees - good thing I never released that one. There seems to be some changes in the event callbacks, or their frequency.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)