3.14: KeyError in sysmon_branch_either after use of except* #2086
Description
Describe the bug
Similar to #1991, a KeyError is emitted from sysmon_branch_either on Python 3.14.0 after a use of except*.
======================================================================
ERROR: test_asgi_cookies (asgi.tests.ASGITest.test_asgi_cookies)
----------------------------------------------------------------------
+ Exception Group Traceback (most recent call last):
| File "/Users/jwalls/.env/lib/python3.14/site-packages/django/core/handlers/asgi.py", line 196, in handle
| async with asyncio.TaskGroup() as tg:
| ~~~~~~~~~~~~~~~~~^^
| File "/Library/Frameworks/Python.framework/Versions/3.14/lib/python3.14/asyncio/taskgroups.py", line 72, in __aexit__
| return await self._aexit(et, exc)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^
| File "/Library/Frameworks/Python.framework/Versions/3.14/lib/python3.14/asyncio/taskgroups.py", line 174, in _aexit
| raise BaseExceptionGroup(
| ...<2 lines>...
| ) from None
| ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
+-+---------------- 1 ----------------
| Traceback (most recent call last):
| File "/Users/jwalls/.env/lib/python3.14/site-packages/django/core/handlers/asgi.py", line 200, in handle
| raise RequestProcessed
| django.core.handlers.asgi.ASGIHandler.handle.<locals>.RequestProcessed
+------------------------------------
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/Users/jwalls/.env/lib/python3.14/site-packages/asgiref/sync.py", line 325, in __call__
return call_result.result()
~~~~~~~~~~~~~~~~~~^^
File "/Library/Frameworks/Python.framework/Versions/3.14/lib/python3.14/concurrent/futures/_base.py", line 443, in result
return self.__get_result()
~~~~~~~~~~~~~~~~~^^
File "/Library/Frameworks/Python.framework/Versions/3.14/lib/python3.14/concurrent/futures/_base.py", line 395, in __get_result
raise self._exception
File "/Users/jwalls/.env/lib/python3.14/site-packages/asgiref/sync.py", line 365, in main_wrap
result = await awaitable
^^^^^^^^^^^^^^^
File "/Users/jwalls/django/tests/asgi/tests.py", line 89, in test_asgi_cookies
await communicator.wait()
File "/Users/jwalls/.env/lib/python3.14/site-packages/asgiref/testing.py", line 58, in wait
await self.future
File "/Users/jwalls/.env/lib/python3.14/site-packages/django/core/handlers/asgi.py", line 166, in __call__
await self.handle(scope, receive, send)
File "/Users/jwalls/.env/lib/python3.14/site-packages/django/core/handlers/asgi.py", line None, in handle
File "/Users/jwalls/.env/lib/python3.14/site-packages/coverage/sysmon.py", line 460, in sysmon_branch_either
l1 = code_info.byte_to_line[instruction_offset]
~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^
KeyError: 916
----------------------------------------------------------------------
Ran 1 test in 0.352sTo Reproduce
Answer the questions below:
- What version of Python are you using? 3.14.0
- What version of coverage.py shows the problem? The output of
coverage debug sysis helpful. 7.11.3
Full debug sys output
-- sys -------------------------------------------------------
coverage_version: 7.11.3
coverage_module: /Users/jwalls/coverage_repro/lib/python3.14/site-packages/coverage/__init__.py
core: -none-
CTracer: available from /Users/jwalls/coverage_repro/lib/python3.14/site-packages/coverage/tracer.cpython-314-darwin.so
plugins.file_tracers: -none-
plugins.configurers: -none-
plugins.context_switchers: -none-
configs_attempted: /Users/jwalls/django/tests/.coveragerc
configs_read: /Users/jwalls/django/tests/.coveragerc
config_file: /Users/jwalls/django/tests/.coveragerc
config_contents: b'[run]\nbranch = True\nconcurrency = multiprocessing,thread\ndata_file = ${RUNTESTS_DIR-.}/.coverages/.coverage\nomit =\n */django/utils/autoreload.py\nsource = django\n\n[report]\nignore_errors = True\nomit =\n */django/conf/locale/*\n */tests/*\n\n[html]\ndirectory = coverage_html\n'
data_file: -none-
python: 3.14.0 (v3.14.0:ebf955df7a8, Oct 7 2025, 08:20:14) [Clang 16.0.0 (clang-1600.0.26.6)]
platform: macOS-26.1-arm64-arm-64bit-Mach-O
implementation: CPython
build: v3.14.0:ebf955df7a8
Oct 7 2025 08:20:14
gil_enabled: True
executable: /Users/jwalls/coverage_repro/bin/python
def_encoding: utf-8
fs_encoding: utf-8
pid: 36810
cwd: /Users/jwalls/django/tests
path: /Users/jwalls/django/tests
/Library/Frameworks/Python.framework/Versions/3.14/lib/python314.zip
/Library/Frameworks/Python.framework/Versions/3.14/lib/python3.14
/Library/Frameworks/Python.framework/Versions/3.14/lib/python3.14/lib-dynload
/Users/jwalls/coverage_repro/lib/python3.14/site-packages
environment: BUNDLED_DEBUGPY_PATH = /Users/jwalls/.vscode/extensions/ms-python.debugpy-2025.15.2025110501-darwin-arm64/bundled/libs/debugpy
HOME = /Users/jwalls
PYDEVD_DISABLE_FILE_VALIDATION = 1
PYTHONSTARTUP = /Users/jwalls/Library/Application Support/Code/User/workspaceStorage/ce83212064299361443b563749bd458d/ms-python.python/pythonrc.py
PYTHON_BASIC_REPL = 1
VSCODE_DEBUGPY_ADAPTER_ENDPOINTS = /Users/jwalls/.vscode/extensions/ms-python.debugpy-2025.15.2025110501-darwin-arm64/.noConfigDebugAdapterEndpoints/endpoint-69acd048cfc652fa.txt
VSCODE_PYTHON_AUTOACTIVATE_GUARD = 1
command_line: /Users/jwalls/coverage_repro/lib/python3.14/site-packages/coverage/__main__.py debug sys
time: 2025-11-13 17:11:12
- What versions of what packages do you have installed? The output of
pip freezeis helpful.
asgiref==3.10.0
coverage==7.11.3
Django @ file:///Users/jwalls/django
sqlparse==0.5.3
- What code shows the problem? Give us a specific commit of a specific repo that we can check out. If you've already worked around the problem, please provide a commit before that fix.
We isolated the triggering code to django/django@2501958 and almost certainly the line containing except*.
- What commands should we run to reproduce the problem? Be specific. Include everything, even
git clone,pip install, and so on. Explain like we're five!
python -m venv .env
source .env/bin/activate
git clone https://github.com/django/django
cd django
git checkout 2501958b5127020411df6271445ccfd0906df70e
pip install .
pip install coverage
cd tests
python -m coverage run runtests.py asgi.tests.ASGITest.test_asgi_cookies
Expected behavior
Successful coverage run
Additional context
We isolated the triggering code to django/django@2501958 and almost certainly the line containing except*.