Summary

Fix DeprecationWarning while spying on generator functions.

Review Request #14574 — Created Aug. 28, 2025 and submitted Nov. 5, 2025, 9:58 a.m.

Information

Owner

david

Repository

kgb

Branch

master

Bugs

Depends On

Reviewers

Groups

kgb

People

Description

Python 3.13 added a new DeprecationWarning which is triggered when

calling setattr() to replace the code object of a function in the case

that the code object's flags have a mismatch on the CO_GENERATOR,

CO_COROUTINE, or CO_ASYNC_GENERATOR bits. This was done in response

to a bug (https://github.com/python/cpython/issues/81137) where

replacing a lambda's code object with the gi_code attribute from a

generator expression would then cause cpython to crash. This was purely

a problem with the way that gi_code works for generator expressions

(and comprehensions), and does not affect generator functions in the

same way. This means that rather than posing a real issue for kgb, we

just see ugly warnings.
In order to prevent these warnings, we now copy true values for those

three flags from the old code object into the new one.

Testing Done


Commented out the fix and saw the new unit test fail.
Ran unit tests and saw no more warnings.
Tested with an experimental test (not included here) that replaces an

  async generator and saw that that worked too.
Ran tests on Python 3.8-3.13

Commits

Summary	ID
Fix DeprecationWarning while spying on generator functions. Python 3.13 added a new `DeprecationWarning` which is triggered when calling `setattr()` to replace the code object of a function in the case that the code object's flags have a mismatch on the `CO_GENERATOR`, `CO_COROUTINE`, or `CO_ASYNC_GENERATOR` bits. This was done in response to a bug (https://github.com/python/cpython/issues/81137) where replacing a lambda's code object with the `gi_code` attribute from a generator expression would then cause cpython to crash. This was purely a problem with the way that `gi_code` works for generator expressions (and comprehensions), and does not affect generator functions in the same way. This means that rather than posing a real issue for kgb, we just see ugly warnings. In order to prevent these warnings, we now copy true values for those three flags from the old code object into the new one. Testing Done: - Commented out the fix and saw the new unit test fail. - Ran unit tests and saw no more warnings. - Tested with an experimental test (not included here) that replaces an async generator and saw that that worked too. - Ran tests on Python 3.8-3.13	nlputqsrwlmlwnrnzwsrzqzxqqxwoqpm

Summary

Fix DeprecationWarning while spying on generator functions.

Python 3.13 added a new `DeprecationWarning` which is triggered when calling `setattr()` to replace the code object of a function in the case that the code object's flags have a mismatch on the `CO_GENERATOR`, `CO_COROUTINE`, or `CO_ASYNC_GENERATOR` bits. This was done in response to a bug (https://github.com/python/cpython/issues/81137) where replacing a lambda's code object with the `gi_code` attribute from a generator expression would then cause cpython to crash. This was purely a problem with the way that `gi_code` works for generator expressions (and comprehensions), and does not affect generator functions in the same way. This means that rather than posing a real issue for kgb, we just see ugly warnings. In order to prevent these warnings, we now copy true values for those three flags from the old code object into the new one. Testing Done: - Commented out the fix and saw the new unit test fail. - Ran unit tests and saw no more warnings. - Tested with an experimental test (not included here) that replaces an async generator and saw that that worked too. - Ran tests on Python 3.8-3.13

nlputqsrwlmlwnrnzwsrzqzxqqxwoqpm

Issues

Description	From	Last Updated
Can you verify (and include in Testing Done) whether all Python versions pass via tox?	chipx86	Sept. 4, 2025, 10:22 p.m.
Can you add a blank line before that URL? This looks unbalanced.	chipx86	Sept. 4, 2025, 10:21 p.m.
"CPython"	chipx86	Sept. 4, 2025, 10:21 p.m.
Can we do one per line?	chipx86	Sept. 4, 2025, 10:21 p.m.

flake8 passed.

JSHint passed.

Ship it!

```
Ship It!
```

The issue has been resolved. Show all issues

Can you verify (and include in Testing Done) whether all Python versions pass via tox?

david Sept. 4, 2025, 10:25 p.m.

For some reason running through tox isn't working, but I manually verified 3.8-3.13.

Did discover that this fix breaks < 3.11 as a result though, so thanks for the push.

kgb/spies.py (Diff revision 1)

The issue has been resolved. Show all issues

Can you add a blank line before that URL? This looks unbalanced.

kgb/spies.py (Diff revision 1)
The issue has been resolved. Show all issues
```
"CPython"
```
kgb/spies.py (Diff revision 1)
The issue has been resolved. Show all issues
```
Can we do one per line?
```

Testing Done:

		Commented out the fix and saw the new unit test fail.
		Ran unit tests and saw no more warnings.
		Tested with an experimental test (not included here) that replaces an async generator and saw that that worked too.
	+	Ran tests on Python 3.8-3.13

Commits:

	Summary	ID
	Fix DeprecationWarning while spying on generator functions. Python 3.13 added a new `DeprecationWarning` which is triggered when calling `setattr()` to replace the code object of a function in the case that the code object's flags have a mismatch on the `CO_GENERATOR`, `CO_COROUTINE`, or `CO_ASYNC_GENERATOR` bits. This was done in response to a bug (https://github.com/python/cpython/issues/81137) where replacing a lambda's code object with the `gi_code` attribute from a generator expression would then cause cpython to crash. This was purely a problem with the way that `gi_code` works for generator expressions (and comprehensions), and does not affect generator functions in the same way. This means that rather than posing a real issue for kgb, we just see ugly warnings. In order to prevent these warnings, we now copy true values for those three flags from the old code object into the new one. Testing Done: - Commented out the fix and saw the new unit test fail. - Ran unit tests and saw no more warnings. - Tested with an experimental test (not included here) that replaces an async generator and saw that that worked too.	zqxoklumwxzuwspwlvnwwrqmomxznppt
	Fix DeprecationWarning while spying on generator functions. Python 3.13 added a new `DeprecationWarning` which is triggered when calling `setattr()` to replace the code object of a function in the case that the code object's flags have a mismatch on the `CO_GENERATOR`, `CO_COROUTINE`, or `CO_ASYNC_GENERATOR` bits. This was done in response to a bug (https://github.com/python/cpython/issues/81137) where replacing a lambda's code object with the `gi_code` attribute from a generator expression would then cause cpython to crash. This was purely a problem with the way that `gi_code` works for generator expressions (and comprehensions), and does not affect generator functions in the same way. This means that rather than posing a real issue for kgb, we just see ugly warnings. In order to prevent these warnings, we now copy true values for those three flags from the old code object into the new one. Testing Done: - Commented out the fix and saw the new unit test fail. - Ran unit tests and saw no more warnings. - Tested with an experimental test (not included here) that replaces an async generator and saw that that worked too. - Ran tests on Python 3.8-3.13	nlputqsrwlmlwnrnzwsrzqzxqqxwoqpm

Diff:

Revision 2 (+122 -6)

Show changes

	kgb/spies.py
	kgb/tests/test_function_spy.py

Checks run (2 succeeded)

flake8 passed.

JSHint passed.

Ship it!

```
Ship It!
```

Status:: Completed
Change Summary:: Pushed to master (d549103)