python-crypto fails to build with Python 3.10.0a2.

Traceback (most recent call last):
  File "build/lib.linux-x86_64-3.10/Crypto/SelfTest/Cipher/common.py", line 206, in runTest
    cipher = self.module.new(a2b_hex(self.key), self.module.MODE_CTR, counter=ctr)
  File "build/lib.linux-x86_64-3.10/Crypto/Cipher/AES.py", line 95, in new
    return AESCipher(key, *args, **kwargs)
  File "build/lib.linux-x86_64-3.10/Crypto/Cipher/AES.py", line 59, in __init__
    blockalgo.BlockAlgo.__init__(self, _AES, key, *args, **kwargs)
  File "build/lib.linux-x86_64-3.10/Crypto/Cipher/blockalgo.py", line 139, in __init__
    self._cipher = factory.new(key, *args, **kwargs)
SystemError: PY_SSIZE_T_CLEAN macro must be defined for '#' formats

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-parsing
https://www.python.org/dev/peps/pep-0353
https://bugs.python.org/issue40943

For the build logs, see:
https://copr-be.cloud.fedoraproject.org/results/@python/python3.10/fedora-rawhide-x86_64/01757388-python-crypto/

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

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.