[New-bugs-announce] [issue44050] Exceptions in a subinterpreter are changed by another subinterpreter

Trygve Aaberge report at bugs.python.org
Wed May 5 10:22:11 EDT 2021

New submission from Trygve Aaberge <trygveaa at gmail.com>:

This issue is a regression in Python 3.9. It was recently fixed in main/3.10, but I'm opening this issue to request that it is fixed in 3.9 as well since it breaks certain Python scripts running in WeeChat.

I have a C application which is using the Python/C API and is running multiple python subinterpreters. One of those subinterpreters is running a script which is reading data from a non-blocking ssl socket. When there is no more data to read, trying to read throws `ssl.SSLWantReadError` which is handled by the script. However, if a script in another subinterpreter imports _ssl, the SSLWantReadError exceptions thrown in the first script now have a different class instance, so they are not catched anymore.

This is a regression in 3.9. It didn't happen in 3.8. The commit that introduced the issue is https://github.com/python/cpython/commit/82c83bd907409c287a5bd0d0f4598f2c0538f34d
The commit that fixes the issue in 3.10 is https://github.com/python/cpython/commit/7f1305ef9ea7234e1a5aacbea17490232e9b7dc2

I have attached a C program to reproduce the issue. It seems I can only attach one file per comment, so the python script that program runs will follow in the next commit. It connects to an ssl socket, so you need to have that running first. That can be started by running this:

openssl req -x509 -nodes -newkey rsa:4096 -keyout key.pem -out cert.pem -days 365 -subj '/'
openssl s_server -key key.pem -cert cert.pem -accept 1234

The script will output this when the issue is not present (so in 3.8 and main):
no data
no data

And this when the issue is present (in 3.9):
no dataunknown error: The operation did not complete (read) (_ssl.c:2627)
exception name: SSLWantReadError
SSLWantReadError id: 93893206532320
exception id: 93893207118800

components: Subinterpreters
files: interpreter.c
messages: 393011
nosy: trygveaa
priority: normal
severity: normal
status: open
title: Exceptions in a subinterpreter are changed by another subinterpreter
type: behavior
versions: Python 3.9
Added file: https://bugs.python.org/file50015/interpreter.c

Python tracker <report at bugs.python.org>

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