List comprehensions cause subinterpreter crashes

[ZeroIntensity]

Crash report

What happened?

If you use any list comprehension inside a subinterpreter (either through _interpreters or through interpreters), an assertion fails in _PyCode_CheckNoExternalState:

import _interpreters

interp = _interpreters.create()
_interpreters.run_string(interp, "[None for _ in []]")

python: Objects/codeobject.c:1982: _PyCode_CheckNoExternalState: Assertion `counts->locals.hidden.total == 0' failed.

This was originally causing failures in #134606. I think that assertion can be removed, because _PyCode_CheckNoExternalState seems to have no need for the number of hidden locals being zero.

cc @ericsnowcurrently

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

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

No response

Linked PRs

• gh-135450: Remove assertion in _PyCode_CheckNoExternalState #135466
• [3.14] gh-135450: Remove assertion in _PyCode_CheckNoExternalState (gh-135466) #135694

[ericsnowcurrently]

I added that assertion with the gut instinct that we'd have to remove it. It just wasn't clear to me at the time where to expect hidden variables relative to "external" state in a code object. Comprehensions make sense. Thanks for identifying this.

[ZeroIntensity]

Ok, yeah, that makes sense. I kept staring at that assertion trying to figure out why the function wanted that as a precondition. Thanks for the insight!