SystemError: compiler_lookup_arg(name='name_1') with reftype=7 failed in <genexpr>

@JelleZijlstra

Crash report

What happened?

I found the following issue by fuzzing with pysource-codegen.

This script failed to compile the given code to bytecode:

code="""
(name_3): name_5
name_4: (
    name_4
    async for (
        name_5
        for something in name_1
        async for () in (name_0 async for name_5 in name_0 for name_0 in name_1)
    ).name_3 in {name_5: name_5 for name_1 in name_4}
)
"""
compile(code,"<file>","exec")

running it with cpython results in the following error:

Traceback (most recent call last):
  File "/home/frank/projects/cpython/../pysource-playground/bug.py", line 12, in <module>
    compile(code,"<file>","exec")
    ~~~~~~~^^^^^^^^^^^^^^^^^^^^^^
SystemError: compiler_lookup_arg(name='name_1') with reftype=7 failed in <genexpr>; freevars of code <genexpr>: ('name_1',)

I bisected the problem down to 9b8611e @JelleZijlstra do you want to take a look at it?

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

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

Python 3.14.0a0 (bisect/bad:9b8611eeea1, Apr 13 2025, 17:20:02) [GCC 12.2.0]

Linked PRs

gh-132479: Fix crash with multiple comprehensions in annotations #132778

@carljm

Thanks! Slightly simplified repro (don't need the async):

code="""
x: name_5
name_4: (
    name_4
    for (
        name_5
        for something in name_1
        for () in (name_0 for name_5 in name_0 for name_0 in name_1)
    ).name_3 in {name_5 for name_1 in name_4}
)
"""
compile(code,"<file>","exec")

cc @carljm too since this involves a comprehension. It doesn't repro any more when I change the setcomp to a genexp (which isn't inlined).

I have found two other very similar errors. Perhaps this will help to solve the problem.

name_2: {}
name_0: {
    name_0: name_5
    for name_4 in [name_5 for name_0 in name_1]
    if ((name_0 for name_2 in name_5) for [] in name_1)
}

SystemError: compiler_lookup_arg(name='name_0') with reftype=3 failed in __annotate__; freevars of code <genexpr>: ('name_0',)

[][[]]: {name_4 for name_0 in name_1}
name_2: {
    something: (lambda: name_0 for [] in name_4 for name_2 in name_5)
    for something in ()
    if name_0
    for name_5 in something
}

SystemError: compiler_lookup_arg(name='name_0') with reftype=3 failed in __annotate__; freevars of code <genexpr>: ('name_0', 'name_5')

I would like to investigate this, but I'm afraid I won't realistically have time for it anytime soon, so I would encourage anyone interested to look into it.

@JelleZijlstra

@JelleZijlstra the new version of pysource-minimize can now also remove the await. I just released a new version you can see it here in action.

Please tell me if anyone finds another way how this can be simplified. Maybe it allows me to improve pysource-minimize a bit more.

I found some new minimization.

expressions are replaced with 0 if possible
names are replaced with an unique name if possible

This gave me the following new examples (minimized from the original (not minimized) 3 problems):

(unique_name_0): 0
unique_name_1: (
    0
    for (
        0
        for unique_name_2 in 0
        for () in (0 for unique_name_3 in unique_name_4 for unique_name_5 in name_1)
    ).name_3 in {0: 0 for name_1 in unique_name_8}
    if name_1
)

unique_name_0: 0
unique_name_1: {
    0: 0
    for unique_name_2 in [0 for name_0 in unique_name_4]
    if {
        0: 0
        for unique_name_5 in 0
        if name_0
        if ((name_0 for unique_name_8 in unique_name_9) for [] in 0)
    }
}

0[0]: {0 for name_0 in unique_name_1}
unique_name_2: {
    0: (lambda: name_0 for unique_name_4 in unique_name_5)
    for unique_name_6 in ()
    if name_0
}

pythongh-132479: Fix crash with multiple comprehensions in annotations

I found a fix: #132778. It's definitely in "how did anything work" territory; we were adding the annotation scope to ste_children multiple times, one for each individual module-level annotation. I haven't tracked down exactly why that breaks things, but I guess it has something to do with inline_comprehension() being called multiple times.

gh-132479: Fix crash with multiple comprehensions in annotations (#13…

Thanks for the report!

Thanks for fixing it.

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SystemError: compiler_lookup_arg(name='name_1') with reftype=7 failed in <genexpr> #132479

Crash report

What happened?

CPython versions tested on:

Operating systems tested on:

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

Linked PRs

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SystemError: compiler_lookup_arg(name='name_1') with reftype=7 failed in <genexpr> #132479

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

JelleZijlstra commented on Apr 13, 2025

15r10nk commented on Apr 14, 2025

carljm commented on Apr 14, 2025

15r10nk commented on Apr 16, 2025

15r10nk commented on Apr 16, 2025

JelleZijlstra commented on Apr 21, 2025

JelleZijlstra commented on Apr 21, 2025

15r10nk commented on Apr 22, 2025

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