Import fails on Python 3.10.0b1

[mattclay]

Python 3.10.0b1 (default, May  6 2021, 02:44:57) [GCC 7.5.0] on linux
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>>> import spnego
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/tmp/demo/lib/python3.10/site-packages/spnego/__init__.py", line 12, in <module>
    from spnego._context import (
  File "/tmp/demo/lib/python3.10/site-packages/spnego/_context.py", line 37, in <module>
    from spnego.iov import (
  File "/tmp/demo/lib/python3.10/site-packages/spnego/iov.py", line 14, in <module>
    class BufferType(IntFlag):
  File "/usr/lib/python3.10/enum.py", line 544, in __new__
    raise TypeError(
TypeError: invalid Flag 'BufferType' -- missing values: 4, 8

This appears to be due to this change in CPython: python/cpython#24215

[jborean93]

Hmm I saw this when trying out the alpha and I hoped it would not be the case on the beta but obviously not. This personally seems like a breaking change on their part and I cannot understand the reasons why this is not required. I’ll have to try and follow it up.

[jborean93]

So I was wrong, I was mistakenly using IntFlag instead of IntEnum here causing the problems. The field is a single value so shouldn't be IntFlag and is the reason why it's complaining that 4 and 8 were missing.