gh-132775: Add _PyCode_VerifyStateless()

[ericsnowcurrently]

"Stateless" code is a function or code object which does not rely on external state or internal state. It may rely on arguments and
builtins, but not globals or a closure. I've left a comment in pycore_code.h that provides more detail.

We also add _PyFunction_VerifyStateless(). The new functions will be used in several later changes that facilitate "sharing" functions and code objects between interpreters.

• Issue: Improvements to test.support.interpreters.Interpreter #132775

[ericsnowcurrently]

!buildbot s390x RHEL8 LTO + PGO

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @ericsnowcurrently for commit d45c0e0 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F133221%2Fmerge

The command will test the builders whose names match following regular expression: s390x RHEL8 LTO \+ PGO

The builders matched are:

• s390x RHEL8 LTO + PGO PR

[neonene]

Is the warning on Windows fixable on this PR?

[ericsnowcurrently]

fixed

[nascheme]

This looks to be failing on the iOS buildbot.

test_code (test)
Doctest: test.test_code ... ok
======================================================================
ERROR: test_stateless (test.test_code.CodeTest.test_stateless) [(<function spam_N at 0x10fab5b50>, '(code)')]
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/buildbot/Library/Developer/XCTestDevices/3749308D-3FDE-41E4-B27C-3A4DD1FCF87A/data/Containers/Bundle/Application/40457EBF-BF74-4E58-B5DB-F52F8BC085A9/iOSTestbed.app/python/lib/python3.14/test/test_code.py", line 1049, in test_stateless
    _testinternalcapi.verify_stateless_code(func.__code__)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^
ValueError: only basic code objects are supported
======================================================================
ERROR: test_stateless (test.test_code.CodeTest.test_stateless) [(<function spam_C at 0x10fab4a10>, '(code)')]
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/buildbot/Library/Developer/XCTestDevices/3749308D-3FDE-41E4-B27C-3A4DD1FCF87A/data/Containers/Bundle/Application/40457EBF-BF74-4E58-B5DB-F52F8BC085A9/iOSTestbed.app/python/lib/python3.14/test/test_code.py", line 1049, in test_stateless
    _testinternalcapi.verify_stateless_code(func.__code__)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^
ValueError: only basic code objects are supported

https://buildbot.python.org/#/builders/1380/builds/3582/

[encukou]

The test fails when it's run twice:

./python -m test test_code test_code

[encukou]

Looks like setting sys.settrace with opcode tracing causes all code to be instrumented when it's next run.

import sys
import _testinternalcapi

def foo():
    pass

def trace_temporarily():
    sys._getframe().f_trace_opcodes = True
    sys.settrace(print)
    sys.settrace(None)
    sys._getframe().f_trace_opcodes = False
trace_temporarily()

_testinternalcapi.verify_stateless_code(foo.__code__)
foo()
_testinternalcapi.verify_stateless_code(foo.__code__)  # fails

In this case, test_code_equal_with_instrumentation does this. If it runs first, then some test that exepcutes the tested functions (to get the closures I guess), then test_stateless will fail.

[encukou]

I'm not sure what exactly "statelessness" is used for in the subinterpreters code. But, it looks like if it is to be useful, it either

• needs to be treated as an important property that can't be broken by optimizations, or
• the function should be _PyCode_IsStateless, returning a bool, with typical users needing to implement a fallback (copying the code object should be enough?)

Unfortunately, given the timing, I think this needs to be reverted for 3.14 :(

[hugovk]

@encukou Please could you open a revert PR?

[encukou]

Will do. Resolving conflicts.

[hugovk]

Reverted in #133497.

[ericsnowcurrently]

Thanks for jumping on this. I'll sort it out. FYI, the relevant code is _PyCode_CheckNoInternalState(). It isn't clear to me how test_code_equal_with_instrumentation is affecting the functions used in test_stateless, but it probably doesn't matter. :)