SIGSEGV in Python 3.14.0rc2+ with List Comprehension and Lambda Expression

Crash report

What happened?

A segmentation fault (SIGSEGV) occurs when executing a list comprehension containing a lambda expression in Python 3.14.0rc2+. The crash is reproducible with a minimal code snippet and does not occur in earlier versions (e.g., Python 3.13).

Description:
The following code causes a segmentation fault in Python 3.14.0rc2+:

def report_error():
    pass
try:
    [0 for name_2 in unique_name_0 if (lambda: name_2)]
except:
    pass
unique_name_1: 0

> ../cpython/install/bin/python3 -X faulthandler  crash.py 
Fatal Python error: Segmentation fault

Current thread 0x00007f056f764740 [python3] (most recent call first):
  File "/home/frank/projects/pysource-playground/crash.py", line 7 in <module>

Current thread's C stack trace (most recent call first):
  Binary file "../cpython/install/bin/python3", at _Py_DumpStack+0x2e [0x55dc00a44c9e]
  Binary file "../cpython/install/bin/python3", at +0x2fd99a [0x55dc00a5999a]
  Binary file "/lib/x86_64-linux-gnu/libc.so.6", at +0x3c050 [0x7f056f7a3050]
  Binary file "../cpython/install/bin/python3", at +0x18624b [0x55dc008e224b]
  Binary file "../cpython/install/bin/python3", at _PyEval_EvalFrameDefault+0x16b8 [0x55dc007e6368]
  Binary file "../cpython/install/bin/python3", at PyEval_EvalCode+0x2c6 [0x55dc009b5016]
  Binary file "../cpython/install/bin/python3", at +0x2cbaee [0x55dc00a27aee]
  Binary file "../cpython/install/bin/python3", at +0x2cd9a4 [0x55dc00a299a4]
  Binary file "../cpython/install/bin/python3", at +0x2ce03c [0x55dc00a2a03c]
  Binary file "../cpython/install/bin/python3", at +0x2fbb89 [0x55dc00a57b89]
  Binary file "../cpython/install/bin/python3", at Py_BytesMain+0x64 [0x55dc00a58234]
  Binary file "/lib/x86_64-linux-gnu/libc.so.6", at +0x2724a [0x7f056f78e24a]
  Binary file "/lib/x86_64-linux-gnu/libc.so.6", at __libc_start_main+0x85 [0x7f056f78e305]
  Binary file "../cpython/install/bin/python3", at _start+0x21 [0x55dc007f6481]
fish: Job 1, '../cpython/install/bin/python3 …' terminated by signal SIGSEGV (Adressbereichsfehler)

I build cpython with:

./configure --prefix=$PWD/install --disable-ipv6
make -j install

The script did not crash but also not terminate when I used --with-pydebug.

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

No response

Linked PRs

It reproduces on 3.15 if you put the whole repro in a file; presumably the annotation at the end is important. I'm bisecting now; the issue description says "3.14.0rc2+" but it goes back at least a little further.

It reproduces for me on main, 3.14rc2 and 3.14rc2+ when I put in a file as well.

The bad commit is 922049b (#131550), perhaps unsurprisingly since the module-level annotation is important to reproduce. I will try to fix.

I found two similar examples, maybe this helps finding the problem:

class Generic:
    pass
try:
    [0 for name_2 in unique_name_0 if (0 for unique_name_1 in unique_name_2 for unique_name_3 in name_2)]
except:
    pass
unique_name_4: 0

class Generic:
    pass
unique_name_0: 0
[0 for name_2 in 0 for unique_name_1 in unique_name_2 if (lambda: name_2)]

pythongh-138349: Fix crash when combining module-level annotation and…

I put up a fix in #138363. Your repros still work if you replace class Generic or def report_error with just x = 1; I think the important part is that there is some name being used early in the module, and variable assignment works just as well as creating a function or class. Thanks for the report!

gh-138349: Fix crash when combining module-level annotation and listc…

pythongh-138349: Fix crash when combining module-level annotation and…

[3.14] gh-138349: Fix crash when combining module-level annotation an…

Thanks again!

Navigation Menu

Repository navigation

SIGSEGV in Python 3.14.0rc2+ with List Comprehension and Lambda Expression #138349

Crash report

What happened?

CPython versions tested on:

Operating systems tested on:

Output from running 'python -VV' on the command line:

Linked PRs

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

SIGSEGV in Python 3.14.0rc2+ with List Comprehension and Lambda Expression #138349

Description

Crash report

What happened?

CPython versions tested on:

Operating systems tested on:

Output from running 'python -VV' on the command line:

Linked PRs

Activity

StanFromIreland commented on Sep 1, 2025

JelleZijlstra commented on Sep 1, 2025

Fidget-Spinner commented on Sep 1, 2025

JelleZijlstra commented on Sep 1, 2025

15r10nk commented on Sep 1, 2025

JelleZijlstra commented on Sep 1, 2025

hugovk commented on Sep 11, 2025

Metadata

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Issue actions