Bug in linecache when raising exceptiongroup that contains `ZeroDivisionError` + other exception.

[jonathanslenders]

Bug report

Consider this code:

from asyncio import run, TaskGroup

async def bad_function():
    raise ZeroDivisionError
async def bad_function2():
    raise KeyError

async def main():
    try:
        async with TaskGroup() as tg:
            tg.create_task(bad_function())
            tg.create_task(bad_function2())

    except* ZeroDivisionError as e:
        breakpoint()


run(main())

Run it on Python 3.11 or 3.12:

--Return--
Traceback (most recent call last):
  File "....py", line 18, in <module>
    run(main())
  File "/home/jonathan/.pyenv/versions/3.11.0/lib/python3.11/asyncio/runners.py", line 190, in run
    return runner.run(main)
           ^^^^^^^^^^^^^^^^
  File "/home/jonathan/.pyenv/versions/3.11.0/lib/python3.11/asyncio/runners.py", line 118, in run
    return self._loop.run_until_complete(task)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/jonathan/.pyenv/versions/3.11.0/lib/python3.11/asyncio/base_events.py", line 650, in run_until_complete
    return future.result()
           ^^^^^^^^^^^^^^^
  File ".....py", line -1, in main
  File "/home/jonathan/.pyenv/versions/3.11.0/lib/python3.11/bdb.py", line 94, in trace_dispatch
    return self.dispatch_return(frame, arg)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/jonathan/.pyenv/versions/3.11.0/lib/python3.11/bdb.py", line 153, in dispatch_return
    self.user_return(frame, arg)
  File "/home/jonathan/.pyenv/versions/3.11.0/lib/python3.11/pdb.py", line 372, in user_return
    self.interaction(frame, None)
  File "/home/jonathan/.pyenv/versions/3.11.0/lib/python3.11/pdb.py", line 434, in interaction
    self.print_stack_entry(self.stack[self.curindex])
  File "/home/jonathan/.pyenv/versions/3.11.0/lib/python3.11/pdb.py", line 1554, in print_stack_entry
    self.format_stack_entry(frame_lineno, prompt_prefix))
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/jonathan/.pyenv/versions/3.11.0/lib/python3.11/bdb.py", line 573, in format_stack_entry
    line = linecache.getline(filename, lineno, frame.f_globals)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/jonathan/.pyenv/versions/3.11.0/lib/python3.11/linecache.py", line 31, in getline
    if 1 <= lineno <= len(lines):
TypeError: '<=' not supported between instances of 'int' and 'NoneType'

One of the exceptions has to be a ZeroDivisionError for it to happen as far as I can see.

Your environment

• CPython versions tested on: 3.11, 3.12
• Operating system and architecture: Linux, M1, arm64

Linked PRs

• gh-101517: Fix missing linenumber for re-raise in except* #101663
• gh-101517: Attach line number to the RERAISE at the end of a try-except* #101768
• gh-101517: bdb should not lookup linecache with lineno=None #101787
• [3.11] gh-101517: make bdb avoid looking up in linecache with lineno=None (GH-101787) #101793
• [3.10] gh-101517: make bdb avoid looking up in linecache with lineno=None (GH-101787) #101794
• gh-101517: propagate lasti with RERAISE 1 in except* handling to get currect line numbers #103529
• gh-101517: Add regression test for entering pdb in try/except* block #103547
• gh-101517: fix line number propagation in code generated for except* #103550
• [3.11] gh-101517: fix line number propagation in code generated for except* (#103550) #103816

[gvanrossum]

Can you produce a repro without asyncio? I suspect you can get this by just raising and catching two errors and then raise an ExceptionGroup. @iritkatriel

[iritkatriel]

It's something to do with a breakpoint as the last thing in an except block.

Without asyncio:

excs = []
try:
    raise ZeroDivisionError
except Exception as e:
    excs.append(e)

try:
    raise KeyError
except Exception as e:
    excs.append(e)


def main():
    try:
        raise ExceptionGroup("eg", excs)
    except* ZeroDivisionError as e:
        breakpoint()
        # pass    # <-- uncomment this and the problem goes away

main()

[iritkatriel]

Something to do with frame initialisation? @markshannon @brandtbucher

excs = []
try:
    raise ZeroDivisionError
except Exception as e:
    excs.append(e)

try:
    raise KeyError
except Exception as e:
    excs.append(e)

def main():
    try:
        raise ExceptionGroup("eg", excs)
    except* ZeroDivisionError as e:
        #sys._getframe()     # <-- uncomment this and the problem goes away
        breakpoint()


main()

[brandtbucher]

I don't see the problem going away when I add the sys._getframe() call...

[brandtbucher]

This does reproduce the issue for me, though:

try:
    raise ExceptionGroup("eg", [KeyError(), ValueError()])
except* KeyError:
    breakpoint()
    # pass    # <-- uncomment this and the problem goes away

[brandtbucher]

Note that this only reproduces if some exceptions are uncaught (the ValueError, in my above example... turning it into a KeyError makes the issue go away).

[iritkatriel]

I think it's some kind of heisenbug. I worked around the lineno being None in linecache.py:31, then it failed on None in another place later on, so I added a "print the frame" just before that line, and the problem went away.