Document pdb.post_mortem() accepts exceptions on Python 3.13+

[adamchainz]

Documentation

Some change in Python 3.13 (maybe 5f3433f or related) allows pdb.post_mortem() to accept an exception object, as well as a traceback object. This could be useful to use for chained exception access, for example in Django’s test runner where a traceback is currently passed, but the exception with chained causes is available.

Tested with:

import pdb

try:
    try:
        1 / 0
    except Exception:
        2 / 0
except Exception as exc:
    pdb.post_mortem(exc)

and ran with:

$ uv run -p 3.13 python example.py
> /.../example.py(7)<module>()
-> 2 / 0
(Pdb) exceptions
    0 ZeroDivisionError('division by zero')
>   1 ZeroDivisionError('division by zero')
(Pdb) exceptions 0
> /.../example.py(5)<module>()
-> 1 / 0
(Pdb)

Linked PRs

• gh-128409: Document that pdb.post_mortem() accepts exceptions #128410
• [3.13] gh-128409: Document that pdb.post_mortem() accepts exceptions … #128767

[adamchainz]

pytest is already taking advantage of this “secret feature“: pytest-dev/pytest#12707