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Merged
merged 14 commits into from
Aug 28, 2025
Merged

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

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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
c5b53dc
fix: classmethod __new__
yanyongyu Aug 27, 2025
8a4fb30
chore: update news and add comment
yanyongyu Aug 27, 2025
889e9ec
chore: update news
yanyongyu Aug 27, 2025
3087840
chore: remove unused comment
yanyongyu Aug 27, 2025
67dc247
test: update test cases
yanyongyu Aug 28, 2025
31e28fd
Merge branch 'main' into fix-issue-137317
yanyongyu Aug 28, 2025
e1c11ec
chore: use deco syntax
yanyongyu Aug 28, 2025
43cc52f
Update Lib/test/test_inspect/test_inspect.py
serhiy-storchaka Aug 28, 2025
0e63bd5
Add tests for wrapped metaclass __call__
serhiy-storchaka Aug 28, 2025
8c1f6ef
Renaming.
serhiy-storchaka Aug 28, 2025
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12 changes: 8 additions & 4 deletions Lib/inspect.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1917,17 +1917,21 @@ def _signature_get_user_defined_method(cls, method_name, *, follow_wrapper_chain
if meth is None:
return None

# NOTE: The meth may wraps a non-user-defined callable.
# In this case, we treat the meth as non-user-defined callable too.
# (e.g. cls.__new__ generated by @warnings.deprecated)
unwrapped_meth = None
if follow_wrapper_chains:
meth = unwrap(meth, stop=(lambda m: hasattr(m, "__signature__")
unwrapped_meth = unwrap(meth, stop=(lambda m: hasattr(m, "__signature__")
or _signature_is_builtin(m)))
if isinstance(meth, _NonUserDefinedCallables):

if (isinstance(meth, _NonUserDefinedCallables)
or isinstance(unwrapped_meth, _NonUserDefinedCallables)):
# Once '__signature__' will be added to 'C'-level
# callables, this check won't be necessary
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


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223 changes: 198 additions & 25 deletions Lib/test/test_inspect/test_inspect.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4027,44 +4027,217 @@ 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))
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Should not this be functools.partial(identity(lambda x, a, b: None), 2)? Although the "partial" and "partialmethod" subtests are not affected by all these changes, so I am not sure that it makes sense to keep them. If they do not fail, we cannot be sure that they are meaningful.

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@yanyongyu yanyongyu Aug 28, 2025 •
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Thank you for pointing out the error, I will correct this.

These test cases are based on the ones below (test_signature_on_class_with_init and test_signature_on_class_with_new), and I believe they need to be this detailed to catch potential bugs from changes made in inspect.signature's behavior.


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)

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)

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)

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"),),
...))

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"),),
...))

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
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2025-08-16-16-04-15.gh-issue-137317.Dl13B5.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
:func:`inspect.signature` now correctly handles classes that use a descriptor
on a wrapped :meth:`!__init__` or :meth:`!__new__` method.
Contributed by Yongyu Yan.
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