Python 3.9 support: Python 3.9 was released after Modeller 9.25, but it is largely compatible with Python 3.8, so it can be made to work with Modeller without much effort:
64-bit Windows: download w64_py39_modeller.pyd, go to the directory you installed Modeller in (C:\Program Files\Modeller9.25 by default), go into the lib\x86_64-w64 subdirectory, make a new subdirectory called python3.9, and put the file in there and call it _modeller.pyd. Open Registry Editor, make a new key called HKEY_LOCAL_MACHINE\SOFTWARE\Python\PythonCore\3.9\PythonPath\Modeller9.25 and make it identical to the existing HKEY_LOCAL_MACHINE\SOFTWARE\Python\PythonCore\3.8\PythonPath\Modeller9.25 key.
32-bit Windows: as for 64-bit Windows, but download w32_py39_modeller.pyd instead and put it in the lib\i386-w32\python3.9 subdirectory. The registry key should be called 3.9-32 rather than 3.9.
- Unix tarball: follow the installation instructions for Python 3.8 - they are identical for Python 3.9.
The patches below can be applied to Modeller 9.25 to fix some minor problems. (Use the Unix patch command, or apply them by hand.)
The patches are listed in chronological order (oldest first), so you should apply them in this order to avoid problems.
There are currently no patches for 9.25