Bug#959911: python3.7: No module named '_cffi_backend'

[Yaroslav Halchenko]

Package: python3-cryptography
Version: 2.8-4
Severity: important

I am not sure if it is more pertinent to python3-cffi or one of its packages.

I am still using python3.7 which is AFAIK still supported on sid. But with it,
it fails to import (using it via keyrings module):

$> docker run -it --rm debian:sid
root@c911d74fa6cb:/# apt-get update -qqq; apt-get install -y python3.7 python3-cryptography >/dev/null
debconf: delaying package configuration, since apt-utils is not installed
root@c911d74fa6cb:/# python3.7 -c 'import cryptography.hazmat.primitives.constant_time'
Traceback (most recent call last):
File "<string>", line 1, in <module>
File "/usr/lib/python3/dist-packages/cryptography/hazmat/primitives/constant_time.py", line 11, in <module>
from cryptography.hazmat.bindings._constant_time import lib
ModuleNotFoundError: No module named '_cffi_backend'
root@c911d74fa6cb:/# ls -l /usr/lib/python3/dist-packages/cryptography/hazmat/bindings/
total 824
-rw-r--r-- 1 root root 246 Oct 17 2019 __init__.py
drwxr-xr-x 2 root root 4096 May 6 20:49 __pycache__
-rw-r--r-- 1 root root 14512 Apr 4 22:53 _constant_time.abi3.so
-rw-r--r-- 1 root root 795160 Apr 4 22:53 _openssl.abi3.so
-rw-r--r-- 1 root root 14488 Apr 4 22:53 _padding.abi3.so
drwxr-xr-x 3 root root 4096 May 6 20:48 openssl

it imports fine with python3.8 in sid. I wonder if that is the .abi3 which is
not compatible with python 3.7?

-- System Information:
Debian Release: bullseye/sid
APT prefers testing
APT policy: (900, 'testing'), (600, 'unstable'), (300, 'experimental'), (100, 'unstable-debug'), (100, 'stable-updates'), (100, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 5.5.0-rc5-amd64 (SMP w/12 CPU cores)
Kernel taint flags: TAINT_WARN, TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages python3-cryptography depends on:
ii libc6 2.30-4
ii libssl1.1 1.1.1g-1
ii python3 3.8.2-3
ii python3-cffi-backend [python3-cffi-backend-api-min] 1.14.0-2
pn python3-cffi-backend-api-max <none>
ii python3-six 1.14.0-3

python3-cryptography recommends no packages.

Versions of packages python3-cryptography suggests:
pn python-cryptography-doc <none>
pn python3-cryptography-vectors <none>

-- no debconf information