lib/RELEASE-NOTES contains the following paragraph: * LyX needs to be run under Python 2 and will not work properly on systems where Python 3 is the default binary. See #7030 to know how to fix this properly, since simple shebang conversion in *.py files will not be enough.
I believe that this is a bit misleading. LyX runs fine on systems where the 'python' executable is python 3 as long as python 2 can be called using "python2" (see support/os.cpp). The only known issue is the one found recently by Helge, where a fix is available and just needs confirmation. I am unsure about building LyX where "python" is python 3. We fixed some build scripts to work both with python 2 and 3, but maybe there are others that don't work with python 3 yet. Assuming that Helge confirms the fix for configure.py and it gets in, I would suggest to change the sentence to * LyX needs Python 2 at runtime. On systems where Python 3 is the default python binary it will work as long as a Python 2 interpreter named "python2" is available. Python 2 does still need to be the default binary for building LyX. See #7030 to know how to fix this properly, since simple shebang conversion in *.py files will not be enough. Georg
