Summary

Fix unspy replacing staticmethods and classmethods with plain functions.

Review Request #15147 — Created July 2, 2026 and submitted July 7, 2026, 1:34 p.m.

Information

Owner

david

Repository

kgb

Branch

master

Bugs

Depends On

Reviewers

Groups

kgb

People

Description

When spying on a staticmethod or classmethod defined directly on a

class (passing the method plus owner=), unspy() replaced the

descriptor on the class with a plain function, instead of restoring the

original staticmethod or classmethod.
The cause was in how the spy records the value to restore. When the

owner does not need patching (a class that owns the attribute directly,

not slippery, not inherited), the spy stored self.orig_func as the

restore value. For a staticmethod or classmethod, orig_func is the

function obtained through attribute access, which has already been

unwrapped by the descriptor. On unspy(), that unwrapped function was

assigned back onto the class, discarding the descriptor.
While spied, everything still worked, because the spy swaps the code

object in place and the descriptor keeps pointing at the same function.

The corruption only appeared after unspy(): the attribute was now a

plain function, so a later call through an instance bound the instance

as the first positional argument. For a staticmethod this raised a

TypeError. For a classmethod the instance was silently passed where

the class was expected.
We now store the attribute value exactly as defined in the owner

class dict for this case, matching what the owner-patching path

already does, so the descriptor is preserved across unspy().
This also removes a workaround in the test base class that manually

restored MathClass.class_do_math after each test. That workaround

existed only to paper over this bug, and it corrupted the classmethod

descriptor for later tests. One test

(test_construction_with_call_fake_and_classmethod) depended on that

corruption, asserting object identity across two classmethod accesses;

it now compares by equality, which is correct for a classmethod that

returns a fresh bound method each time.

Testing Done


Commented out the fix and saw the new unit tests fail.
Ran the full test suite on Python 3.14.
Verified all staticmethod and classmethod tests pass in isolation,

  confirming they no longer depend on inter-test state.

Commits

Summary	ID
Fix unspy replacing staticmethods and classmethods with plain functions. When spying on a `staticmethod` or `classmethod` defined directly on a class (passing the method plus `owner=`), `unspy()` replaced the descriptor on the class with a plain function, instead of restoring the original staticmethod or classmethod. The cause was in how the spy records the value to restore. When the owner does not need patching (a class that owns the attribute directly, not slippery, not inherited), the spy stored `self.orig_func` as the restore value. For a staticmethod or classmethod, `orig_func` is the function obtained through attribute access, which has already been unwrapped by the descriptor. On `unspy()`, that unwrapped function was assigned back onto the class, discarding the descriptor. While spied, everything still worked, because the spy swaps the code object in place and the descriptor keeps pointing at the same function. The corruption only appeared after `unspy()`: the attribute was now a plain function, so a later call through an instance bound the instance as the first positional argument. For a staticmethod this raised a `TypeError`. For a classmethod the instance was silently passed where the class was expected. We now store the attribute value exactly as defined in the owner class dict for this case, matching what the owner-patching path already does, so the descriptor is preserved across `unspy()`. This also removes a workaround in the test base class that manually restored `MathClass.class_do_math` after each test. That workaround existed only to paper over this bug, and it corrupted the classmethod descriptor for later tests. One test (`test_construction_with_call_fake_and_classmethod`) depended on that corruption, asserting object identity across two classmethod accesses; it now compares by equality, which is correct for a classmethod that returns a fresh bound method each time. Testing Done: - Commented out the fix and saw the new unit tests fail. - Ran the full test suite on Python 3.14. - Verified all staticmethod and classmethod tests pass in isolation, confirming they no longer depend on inter-test state.	muuzvvoxsvkotspxknnxkttmluwttzvl

Summary

Fix unspy replacing staticmethods and classmethods with plain functions.

When spying on a `staticmethod` or `classmethod` defined directly on a class (passing the method plus `owner=`), `unspy()` replaced the descriptor on the class with a plain function, instead of restoring the original staticmethod or classmethod. The cause was in how the spy records the value to restore. When the owner does not need patching (a class that owns the attribute directly, not slippery, not inherited), the spy stored `self.orig_func` as the restore value. For a staticmethod or classmethod, `orig_func` is the function obtained through attribute access, which has already been unwrapped by the descriptor. On `unspy()`, that unwrapped function was assigned back onto the class, discarding the descriptor. While spied, everything still worked, because the spy swaps the code object in place and the descriptor keeps pointing at the same function. The corruption only appeared after `unspy()`: the attribute was now a plain function, so a later call through an instance bound the instance as the first positional argument. For a staticmethod this raised a `TypeError`. For a classmethod the instance was silently passed where the class was expected. We now store the attribute value exactly as defined in the owner class dict for this case, matching what the owner-patching path already does, so the descriptor is preserved across `unspy()`. This also removes a workaround in the test base class that manually restored `MathClass.class_do_math` after each test. That workaround existed only to paper over this bug, and it corrupted the classmethod descriptor for later tests. One test (`test_construction_with_call_fake_and_classmethod`) depended on that corruption, asserting object identity across two classmethod accesses; it now compares by equality, which is correct for a classmethod that returns a fresh bound method each time. Testing Done: - Commented out the fix and saw the new unit tests fail. - Ran the full test suite on Python 3.14. - Verified all staticmethod and classmethod tests pass in isolation, confirming they no longer depend on inter-test state.

muuzvvoxsvkotspxknnxkttmluwttzvl

Issues

Description	From	Last Updated
Should this be assertIs?	chipx86	July 2, 2026, 5:57 p.m.
This could use SpyOpReturn(0).	chipx86	July 2, 2026, 6:01 p.m.
Same here.	chipx86	July 2, 2026, 6:01 p.m.

flake8 passed.

JSHint passed.

I cannot believe this module full of simple logic and straight-forward behavior would have a bug.

kgb/tests/test_function_spy.py (Diff revision 1)

The issue has been dropped. Show all issues

Should this be assertIs?

david

July 2, 2026, 6:07 p.m.

As per the comment above this, this explicitly cannot be assertIs because classmethod returns a new bound method each time it's accessed.

kgb/tests/test_function_spy.py (Diff revision 1)
The issue has been resolved. Show all issues
```
This could use SpyOpReturn(0).
```
kgb/tests/test_function_spy.py (Diff revision 1)
The issue has been resolved. Show all issues
```
Same here.
```

Commits:

	Summary	ID
	Fix unspy replacing staticmethods and classmethods with plain functions. When spying on a `staticmethod` or `classmethod` defined directly on a class (passing the method plus `owner=`), `unspy()` replaced the descriptor on the class with a plain function, instead of restoring the original staticmethod or classmethod. The cause was in how the spy records the value to restore. When the owner does not need patching (a class that owns the attribute directly, not slippery, not inherited), the spy stored `self.orig_func` as the restore value. For a staticmethod or classmethod, `orig_func` is the function obtained through attribute access, which has already been unwrapped by the descriptor. On `unspy()`, that unwrapped function was assigned back onto the class, discarding the descriptor. While spied, everything still worked, because the spy swaps the code object in place and the descriptor keeps pointing at the same function. The corruption only appeared after `unspy()`: the attribute was now a plain function, so a later call through an instance bound the instance as the first positional argument. For a staticmethod this raised a `TypeError`. For a classmethod the instance was silently passed where the class was expected. We now store the attribute value exactly as defined in the owner class dict for this case, matching what the owner-patching path already does, so the descriptor is preserved across `unspy()`. This also removes a workaround in the test base class that manually restored `MathClass.class_do_math` after each test. That workaround existed only to paper over this bug, and it corrupted the classmethod descriptor for later tests. One test (`test_construction_with_call_fake_and_classmethod`) depended on that corruption, asserting object identity across two classmethod accesses; it now compares by equality, which is correct for a classmethod that returns a fresh bound method each time. Testing Done: - Commented out the fix and saw the new unit tests fail. - Ran the full test suite on Python 3.14. - Verified all staticmethod and classmethod tests pass in isolation, confirming they no longer depend on inter-test state.	muuzvvoxsvkotspxknnxkttmluwttzvl
	Fix unspy replacing staticmethods and classmethods with plain functions. When spying on a `staticmethod` or `classmethod` defined directly on a class (passing the method plus `owner=`), `unspy()` replaced the descriptor on the class with a plain function, instead of restoring the original staticmethod or classmethod. The cause was in how the spy records the value to restore. When the owner does not need patching (a class that owns the attribute directly, not slippery, not inherited), the spy stored `self.orig_func` as the restore value. For a staticmethod or classmethod, `orig_func` is the function obtained through attribute access, which has already been unwrapped by the descriptor. On `unspy()`, that unwrapped function was assigned back onto the class, discarding the descriptor. While spied, everything still worked, because the spy swaps the code object in place and the descriptor keeps pointing at the same function. The corruption only appeared after `unspy()`: the attribute was now a plain function, so a later call through an instance bound the instance as the first positional argument. For a staticmethod this raised a `TypeError`. For a classmethod the instance was silently passed where the class was expected. We now store the attribute value exactly as defined in the owner class dict for this case, matching what the owner-patching path already does, so the descriptor is preserved across `unspy()`. This also removes a workaround in the test base class that manually restored `MathClass.class_do_math` after each test. That workaround existed only to paper over this bug, and it corrupted the classmethod descriptor for later tests. One test (`test_construction_with_call_fake_and_classmethod`) depended on that corruption, asserting object identity across two classmethod accesses; it now compares by equality, which is correct for a classmethod that returns a fresh bound method each time. Testing Done: - Commented out the fix and saw the new unit tests fail. - Ran the full test suite on Python 3.14. - Verified all staticmethod and classmethod tests pass in isolation, confirming they no longer depend on inter-test state.	muuzvvoxsvkotspxknnxkttmluwttzvl

Diff:

Revision 2 (+120 -4)

Show changes

	kgb/spies.py
	kgb/tests/base.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 (639860e)