botan fails to build with Python 3.10.0a2.

src/wrap/python/core.cpp:192:59:   required from here
/usr/include/boost/python/object/make_instance.hpp:50:13: error: lvalue required as left operand of assignment
   50 |             Py_SIZE(instance) = offsetof(instance_t, storage);
      |             ^~~~~~~

https://docs.python.org/3.10/whatsnew/3.10.html#id2

The PY_SSIZE_T_CLEAN macro must now be defined to use PyArg_ParseTuple() and Py_BuildValue() formats which use #: es#, et#, s#, u#, y#, z#, U# and Z#. See Parsing arguments and building values and the PEP 353.
https://docs.python.org/3.10/c-api/arg.html#arg-parsinghttps://www.python.org/dev/peps/pep-0353https://bugs.python.org/issue40943

For the build logs, see:
https://copr-be.cloud.fedoraproject.org/results/@python/python3.10/fedora-rawhide-x86_64/01756966-botan/

For all our attempts to build botan with Python 3.10, see:
https://copr.fedorainfracloud.org/coprs/g/python/python3.10/package/botan/

Testing and mass rebuild of packages is happening in copr. You can follow these instructions to test locally in mock if your package builds with Python 3.10:
https://copr.fedorainfracloud.org/coprs/g/python/python3.10/

Let us know here if you have any questions.

Python 3.10 will be included in Fedora 35. To make that update smoother, we're building Fedora packages with early pre-releases of Python 3.10.
A build failure prevents us from testing all dependent packages (transitive [Build]Requires), so if this package is required a lot, it's important for us to get it fixed soon.
We'd appreciate help from the people who know this package best, but if you don't want to work on this now, let us know so we can try to work around it on our side.