Skip to content

gh-137317: fix inspect signature of class with descriptor wrapper #137862

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 4 commits into
base: main
Choose a base branch
from
+202 −27
Open

gh-137317: fix inspect signature of class with descriptor wrapper #137862

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
cbab1ea
fix: unwrap descriptor get result
yanyongyu Aug 16, 2025
dca94be
test: add decorated tests
yanyongyu Aug 16, 2025
9541a02
chore: add news entry
yanyongyu Aug 16, 2025
d6eb10d
Merge branch 'python:main' into fix-issue-137317
yanyongyu Aug 23, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 0 additions & 2 deletions Lib/inspect.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1926,8 +1926,6 @@ def _signature_get_user_defined_method(cls, method_name, *, follow_wrapper_chain
return None
if method_name != '__new__':
meth = _descriptor_get(meth, cls)
if follow_wrapper_chains:
meth = unwrap(meth, stop=lambda m: hasattr(m, "__signature__"))
return meth


Expand Down
225 changes: 200 additions & 25 deletions Lib/test/test_inspect/test_inspect.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -4027,44 +4027,219 @@ def __init__(self, b):
('bar', 2, ..., "keyword_only")),
...))

def test_signature_on_class_with_decorated_new(self):
def test_signature_on_class_with_decorated_init(self):
def identity(func):
@functools.wraps(func)
def wrapped(*args, **kwargs):
return func(*args, **kwargs)
return wrapped

class Foo:
class C:
@identity
def __new__(cls, a, b):
def __init__(self, b):
pass

self.assertEqual(self.signature(Foo),
((('a', ..., ..., "positional_or_keyword"),
('b', ..., ..., "positional_or_keyword")),
...))
C(1) # does not raise
self.assertEqual(self.signature(C),
((('b', ..., ..., "positional_or_keyword"),),
...))

self.assertEqual(self.signature(Foo.__new__),
((('cls', ..., ..., "positional_or_keyword"),
('a', ..., ..., "positional_or_keyword"),
('b', ..., ..., "positional_or_keyword")),
...))
with self.subTest('classmethod'):
class C:
@classmethod
@identity
def __init__(cls, b):
pass

class Bar:
__new__ = identity(object.__new__)
C(1) # does not raise
self.assertEqual(self.signature(C),
((('b', ..., ..., "positional_or_keyword"),),
...))

varargs_signature = (
(('args', ..., ..., 'var_positional'),
('kwargs', ..., ..., 'var_keyword')),
...,
)
with self.subTest('staticmethod'):
class C:
@staticmethod
@identity
def __init__(b):
pass

C(1) # does not raise
self.assertEqual(self.signature(C),
((('b', ..., ..., "positional_or_keyword"),),
...))

with self.subTest('MethodType'):
class A:
@identity
def call(self, a):
pass

class C:
__init__ = A().call

C(1) # does not raise
self.assertEqual(self.signature(C),
((('a', ..., ..., "positional_or_keyword"),),
...))

with self.subTest('partial'):
class C:
__init__ = identity(functools.partial(lambda x, a, b: None, 2))

C(1) # does not raise
self.assertEqual(self.signature(C),
((('b', ..., ..., "positional_or_keyword"),),
...))

with self.subTest('partialmethod'):
class C:
@identity
def _init(self, x, a):
self.a = (x, a)
__init__ = functools.partialmethod(_init, 2)

self.assertEqual(C(1).a, (2, 1))
self.assertEqual(self.signature(C),
((('a', ..., ..., "positional_or_keyword"),),
...))

class Desc:
def __init__(self, func):
self.func = identity(func)

def __get__(self, instance, owner):
return self.func.__get__(instance, owner)

with self.subTest('descriptor'):
class C:
__init__ = Desc(lambda self, a: None)

self.assertEqual(self.signature(Bar), ((), ...))
self.assertEqual(self.signature(Bar.__new__), varargs_signature)
self.assertEqual(self.signature(Bar, follow_wrapped=False),
varargs_signature)
self.assertEqual(self.signature(Bar.__new__, follow_wrapped=False),
varargs_signature)
C(1) # does not raise
self.assertEqual(self.signature(C),
((('a', ..., ..., "positional_or_keyword"),),
...))

self.assertEqual(self.signature(C.__init__),
((('self', ..., ..., "positional_or_keyword"),
('a', ..., ..., "positional_or_keyword")),
...))

varargs_signature = (
(('args', ..., ..., 'var_positional'),
('kwargs', ..., ..., 'var_keyword')),
...,
)
self.assertEqual(self.signature(C, follow_wrapped=False),
varargs_signature)
self.assertEqual(self.signature(C.__new__, follow_wrapped=False),
varargs_signature)


def test_signature_on_class_with_decorated_new(self):
def identity(func):
@functools.wraps(func)
def wrapped(*args, **kwargs):
return func(*args, **kwargs)
return wrapped

with self.subTest('FunctionType'):
class C:
@identity
def __new__(cls, a):
return a

self.assertEqual(C(1), 1)
self.assertEqual(self.signature(C),
((('a', ..., ..., "positional_or_keyword"),),
...))

# TODO: classmethod is not correct
# with self.subTest('classmethod'):
# class C:
# @classmethod
# @identity
# def __new__(cls, cls2, a):
# return a

# self.assertEqual(C(1), 1)
# self.assertEqual(self.signature(C),
# ((('a', ..., ..., "positional_or_keyword"),),
# ...))

with self.subTest('staticmethod'):
class C:
@staticmethod
@identity
def __new__(cls, a):
return a

self.assertEqual(C(1), 1)
self.assertEqual(self.signature(C),
((('a', ..., ..., "positional_or_keyword"),),
...))

# TODO: method type is not correct
# with self.subTest('MethodType'):
# class A:
# @identity
# def call(self, cls, a):
# return a
# class C:
# __new__ = A().call

# self.assertEqual(C(1), 1)
# self.assertEqual(self.signature(C),
# ((('a', ..., ..., "positional_or_keyword"),),
# ...))

with self.subTest('partial'):
class C:
__new__ = identity(functools.partial(lambda x, cls, a: (x, a), 2))

self.assertEqual(C(1), (2, 1))
self.assertEqual(self.signature(C),
((('a', ..., ..., "positional_or_keyword"),),
...))

with self.subTest('partialmethod'):
class C:
__new__ = functools.partialmethod(identity(lambda cls, x, a: (x, a)), 2)

self.assertEqual(C(1), (2, 1))
self.assertEqual(self.signature(C),
((('a', ..., ..., "positional_or_keyword"),),
...))

class Desc:
def __init__(self, func):
self.func = identity(func)

def __get__(self, instance, owner):
return self.func.__get__(instance, owner)

with self.subTest('descriptor'):
class C:
__new__ = Desc(lambda cls, a: a)

self.assertEqual(C(1), 1)
self.assertEqual(self.signature(C),
((('a', ..., ..., "positional_or_keyword"),),
...))

self.assertEqual(self.signature(C.__new__),
((('cls', ..., ..., "positional_or_keyword"),
('a', ..., ..., "positional_or_keyword")),
...))

varargs_signature = (
(('args', ..., ..., 'var_positional'),
('kwargs', ..., ..., 'var_keyword')),
...,
)
self.assertEqual(self.signature(C, follow_wrapped=False),
varargs_signature)
self.assertEqual(self.signature(C.__new__, follow_wrapped=False),
varargs_signature)

def test_signature_on_class_with_init(self):
class C:
Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2025-08-16-16-04-15.gh-issue-137317.Dl13B5.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix the behavior when using :func:`inspect.signature` to get the signature
for a class that uses descriptor on a wrapped :meth:`!__init__` methods.
Loading