About Python 3.x
Is the latest and greatest release of Python.
We are all very happy and excited about it and welcome the new stuff and changes it brings to us.
But: it is (intentionally) not compatible with code written for Python 2.x (like MoinMoin).
Moin and Python 3.x
Moin 1.9.x does not support Python 3.x and only works with Python 2.7.x (and we won't port it to py3).
Moin 2.0 is based on Python 3.9+. An alpha version is available, which is not yet suitable for production wikis. Please see: https://github.com/moinwiki/moin/releases.