Python 3.13: test_flatten fails because of the missing traceback poiniting characters

[befeleme]

Describe the incorrect behavior you saw
With Python 3.13.0a3 test_flatten fails.
There's an additional line of output which test doesn't count with

https://github.com/twisted/twisted/blob/12c8a5c8d2a7b4de2c543771997541fe1de87883/src/twisted/web/test/test_flatten.py#L653C1-L667C10

Missing line that fixes this for Python 3.13.0a3

             "Exception while flattening:\n"
             '  File "%s", line %d, in f\n'
             "    g()\n"
+            '    ~^^\n'
             '  File "%s", line %d, in g\n'
             '    raise RuntimeError("reason")\n'
             "RuntimeError: reason\n"

Testing environment

• Fedora Linux 40, context of the RPM build
• Twisted version 23.10.0

[adiroiban]

Thanks for the report.

There is also this issue for generic traceback formatting #12061

can we merge these issues?

We have this umbrella Issue #11750 to centralize the py3.13 work and decide what order is best to fix these issues and enable the autoamted tests.

[befeleme]

I opened a new issue, because there's an open PR for the #11750 which I tested in my build of twisted. This issue is not mitigated by that fix.
But as to maintain the order in the project, if that helps you, feel free to merge these two. :)