[3.12] gh-101293: Fix support of custom callables and types in inspect.Signature.from_callable() (GH-115530) (GH-116198)

Support callables with the __call__() method and types with
__new__() and __init__() methods set to class methods, static
methods, bound methods, partial functions, and other types of
methods and descriptors.

Add tests for numerous types of callables and descriptors.
(cherry picked from commit 59167c962efcae72e8d88aa4b33062ed3de4f120)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

3 files changed, 438 insertions, 89 deletions

diff --git a/Lib/inspect.py b/Lib/inspect.py
index 76490ea..819ce94 100644
--- a/Lib/inspect.py
+++ b/Lib/inspect.py
@@ -2003,15 +2003,17 @@ def _signature_get_user_defined_method(cls, method_name):
     named ``method_name`` and returns it only if it is a
     pure python function.
     """
-    try:
-        meth = getattr(cls, method_name)
-    except AttributeError:
-        return
+    if method_name == '__new__':
+        meth = getattr(cls, method_name, None)
     else:
-        if not isinstance(meth, _NonUserDefinedCallables):
-            # Once '__signature__' will be added to 'C'-level
-            # callables, this check won't be necessary
-            return meth
+        meth = getattr_static(cls, method_name, None)
+    if meth is None or isinstance(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)
+    return meth
 
 
 def _signature_get_partial(wrapped_sig, partial, extra_args=()):
@@ -2456,6 +2458,15 @@ def _signature_from_function(cls, func, skip_bound_arg=True,
                __validate_parameters__=is_duck_function)
 
 
+def _descriptor_get(descriptor, obj):
+    if isclass(descriptor):
+        return descriptor
+    get = getattr(type(descriptor), '__get__', _sentinel)
+    if get is _sentinel:
+        return descriptor
+    return get(descriptor, obj, type(obj))
+
+
 def _signature_from_callable(obj, *,
                              follow_wrapper_chains=True,
                              skip_bound_arg=True,
@@ -2564,7 +2575,6 @@ def _signature_from_callable(obj, *,
         wrapped_sig = _get_signature_of(obj.func)
         return _signature_get_partial(wrapped_sig, obj)
 
-    sig = None
     if isinstance(obj, type):
         # obj is a class or a metaclass
 
@@ -2572,88 +2582,65 @@ def _signature_from_callable(obj, *,
         # in its metaclass
         call = _signature_get_user_defined_method(type(obj), '__call__')
         if call is not None:
-            sig = _get_signature_of(call)
-        else:
-            factory_method = None
-            new = _signature_get_user_defined_method(obj, '__new__')
-            init = _signature_get_user_defined_method(obj, '__init__')
-
-            # Go through the MRO and see if any class has user-defined
-            # pure Python __new__ or __init__ method
-            for base in obj.__mro__:
-                # Now we check if the 'obj' class has an own '__new__' method
-                if new is not None and '__new__' in base.__dict__:
-                    factory_method = new
-                    break
-                # or an own '__init__' method
-                elif init is not None and '__init__' in base.__dict__:
-                    factory_method = init
-                    break
+            return _get_signature_of(call)
 
-            if factory_method is not None:
-                sig = _get_signature_of(factory_method)
-
-        if sig is None:
-            # At this point we know, that `obj` is a class, with no user-
-            # defined '__init__', '__new__', or class-level '__call__'
-
-            for base in obj.__mro__[:-1]:
-                # Since '__text_signature__' is implemented as a
-                # descriptor that extracts text signature from the
-                # class docstring, if 'obj' is derived from a builtin
-                # class, its own '__text_signature__' may be 'None'.
-                # Therefore, we go through the MRO (except the last
-                # class in there, which is 'object') to find the first
-                # class with non-empty text signature.
-                try:
-                    text_sig = base.__text_signature__
-                except AttributeError:
-                    pass
-                else:
-                    if text_sig:
-                        # If 'base' class has a __text_signature__ attribute:
-                        # return a signature based on it
-                        return _signature_fromstr(sigcls, base, text_sig)
-
-            # No '__text_signature__' was found for the 'obj' class.
-            # Last option is to check if its '__init__' is
-            # object.__init__ or type.__init__.
-            if type not in obj.__mro__:
-                # We have a class (not metaclass), but no user-defined
-                # __init__ or __new__ for it
-                if (obj.__init__ is object.__init__ and
-                    obj.__new__ is object.__new__):
-                    # Return a signature of 'object' builtin.
-                    return sigcls.from_callable(object)
-                else:
-                    raise ValueError(
-                        'no signature found for builtin type {!r}'.format(obj))
+        new = _signature_get_user_defined_method(obj, '__new__')
+        init = _signature_get_user_defined_method(obj, '__init__')
 
-    elif not isinstance(obj, _NonUserDefinedCallables):
-        # An object with __call__
-        # We also check that the 'obj' is not an instance of
-        # types.WrapperDescriptorType or types.MethodWrapperType to avoid
-        # infinite recursion (and even potential segfault)
-        call = _signature_get_user_defined_method(type(obj), '__call__')
-        if call is not None:
+        # Go through the MRO and see if any class has user-defined
+        # pure Python __new__ or __init__ method
+        for base in obj.__mro__:
+            # Now we check if the 'obj' class has an own '__new__' method
+            if new is not None and '__new__' in base.__dict__:
+                sig = _get_signature_of(new)
+                if skip_bound_arg:
+                    sig = _signature_bound_method(sig)
+                return sig
+            # or an own '__init__' method
+            elif init is not None and '__init__' in base.__dict__:
+                return _get_signature_of(init)
+
+        # At this point we know, that `obj` is a class, with no user-
+        # defined '__init__', '__new__', or class-level '__call__'
+
+        for base in obj.__mro__[:-1]:
+            # Since '__text_signature__' is implemented as a
+            # descriptor that extracts text signature from the
+            # class docstring, if 'obj' is derived from a builtin
+            # class, its own '__text_signature__' may be 'None'.
+            # Therefore, we go through the MRO (except the last
+            # class in there, which is 'object') to find the first
+            # class with non-empty text signature.
             try:
-                sig = _get_signature_of(call)
-            except ValueError as ex:
-                msg = 'no signature found for {!r}'.format(obj)
-                raise ValueError(msg) from ex
-
-    if sig is not None:
-        # For classes and objects we skip the first parameter of their
-        # __call__, __new__, or __init__ methods
-        if skip_bound_arg:
-            return _signature_bound_method(sig)
-        else:
-            return sig
+                text_sig = base.__text_signature__
+            except AttributeError:
+                pass
+            else:
+                if text_sig:
+                    # If 'base' class has a __text_signature__ attribute:
+                    # return a signature based on it
+                    return _signature_fromstr(sigcls, base, text_sig)
+
+        # No '__text_signature__' was found for the 'obj' class.
+        # Last option is to check if its '__init__' is
+        # object.__init__ or type.__init__.
+        if type not in obj.__mro__:
+            # We have a class (not metaclass), but no user-defined
+            # __init__ or __new__ for it
+            if (obj.__init__ is object.__init__ and
+                obj.__new__ is object.__new__):
+                # Return a signature of 'object' builtin.
+                return sigcls.from_callable(object)
+            else:
+                raise ValueError(
+                    'no signature found for builtin type {!r}'.format(obj))
 
-    if isinstance(obj, types.BuiltinFunctionType):
-        # Raise a nicer error message for builtins
-        msg = 'no signature found for builtin function {!r}'.format(obj)
-        raise ValueError(msg)
+    else:
+        # An object with __call__
+        call = getattr_static(type(obj), '__call__', None)
+        if call is not None:
+            call = _descriptor_get(call, obj)
+            return _get_signature_of(call)
 
     raise ValueError('callable {!r} is not supported by signature'.format(obj))
 
diff --git a/Lib/test/test_inspect/test_inspect.py b/Lib/test/test_inspect/test_inspect.py
index 18a7c08..48018fe 100644
--- a/Lib/test/test_inspect/test_inspect.py
+++ b/Lib/test/test_inspect/test_inspect.py
@@ -2779,9 +2779,12 @@ class TestSignatureObject(unittest.TestCase):
 
         # This doesn't work now.
         # (We don't have a valid signature for "type" in 3.4)
+        class ThisWorksNow:
+            __call__ = type
+        # TODO: Support type.
+        self.assertEqual(ThisWorksNow()(1), int)
+        self.assertEqual(ThisWorksNow()('A', (), {}).__name__, 'A')
         with self.assertRaisesRegex(ValueError, "no signature found"):
-            class ThisWorksNow:
-                __call__ = type
             test_callable(ThisWorksNow())
 
         # Regression test for issue #20786
@@ -3323,6 +3326,98 @@ class TestSignatureObject(unittest.TestCase):
                          ((('a', ..., ..., "positional_or_keyword"),),
                           ...))
 
+        with self.subTest('classmethod'):
+            class CM(type):
+                @classmethod
+                def __call__(cls, a):
+                    return a
+            class C(metaclass=CM):
+                def __init__(self, b):
+                    pass
+
+            self.assertEqual(C(1), 1)
+            self.assertEqual(self.signature(C),
+                            ((('a', ..., ..., "positional_or_keyword"),),
+                            ...))
+
+        with self.subTest('staticmethod'):
+            class CM(type):
+                @staticmethod
+                def __call__(a):
+                    return a
+            class C(metaclass=CM):
+                def __init__(self, b):
+                    pass
+
+            self.assertEqual(C(1), 1)
+            self.assertEqual(self.signature(C),
+                            ((('a', ..., ..., "positional_or_keyword"),),
+                            ...))
+
+        with self.subTest('MethodType'):
+            class A:
+                def call(self, a):
+                    return a
+            class CM(type):
+                __call__ = A().call
+            class C(metaclass=CM):
+                def __init__(self, b):
+                    pass
+
+            self.assertEqual(C(1), 1)
+            self.assertEqual(self.signature(C),
+                            ((('a', ..., ..., "positional_or_keyword"),),
+                            ...))
+
+        with self.subTest('partial'):
+            class CM(type):
+                __call__ = functools.partial(lambda x, a: (x, a), 2)
+            class C(metaclass=CM):
+                def __init__(self, b):
+                    pass
+
+            self.assertEqual(C(1), (2, 1))
+            self.assertEqual(self.signature(C),
+                            ((('a', ..., ..., "positional_or_keyword"),),
+                            ...))
+
+        with self.subTest('partialmethod'):
+            class CM(type):
+                __call__ = functools.partialmethod(lambda self, x, a: (x, a), 2)
+            class C(metaclass=CM):
+                def __init__(self, b):
+                    pass
+
+            self.assertEqual(C(1), (2, 1))
+            self.assertEqual(self.signature(C),
+                            ((('a', ..., ..., "positional_or_keyword"),),
+                            ...))
+
+        with self.subTest('BuiltinMethodType'):
+            class CM(type):
+                __call__ = ':'.join
+            class C(metaclass=CM):
+                def __init__(self, b):
+                    pass
+
+            self.assertEqual(C(['a', 'bc']), 'a:bc')
+            # BUG: Returns '<Signature (b)>'
+            with self.assertRaises(AssertionError):
+                self.assertEqual(self.signature(C), self.signature(''.join))
+
+        with self.subTest('MethodWrapperType'):
+            class CM(type):
+                __call__ = (2).__pow__
+            class C(metaclass=CM):
+                def __init__(self, b):
+                    pass
+
+            self.assertEqual(C(3), 8)
+            self.assertEqual(C(3, 7), 1)
+            # BUG: Returns '<Signature (b)>'
+            with self.assertRaises(AssertionError):
+                self.assertEqual(self.signature(C), self.signature((0).__pow__))
+
         class CM(type):
             def __new__(mcls, name, bases, dct, *, foo=1):
                 return super().__new__(mcls, name, bases, dct)
@@ -3384,6 +3479,169 @@ class TestSignatureObject(unittest.TestCase):
                            ('bar', 2, ..., "keyword_only")),
                           ...))
 
+    def test_signature_on_class_with_init(self):
+        class C:
+            def __init__(self, b):
+                pass
+
+        C(1)  # does not raise
+        self.assertEqual(self.signature(C),
+                        ((('b', ..., ..., "positional_or_keyword"),),
+                        ...))
+
+        with self.subTest('classmethod'):
+            class C:
+                @classmethod
+                def __init__(cls, b):
+                    pass
+
+            C(1)  # does not raise
+            self.assertEqual(self.signature(C),
+                            ((('b', ..., ..., "positional_or_keyword"),),
+                            ...))
+
+        with self.subTest('staticmethod'):
+            class C:
+                @staticmethod
+                def __init__(b):
+                    pass
+
+            C(1)  # does not raise
+            self.assertEqual(self.signature(C),
+                            ((('b', ..., ..., "positional_or_keyword"),),
+                            ...))
+
+        with self.subTest('MethodType'):
+            class A:
+                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__ = functools.partial(lambda x, a: None, 2)
+
+            C(1)  # does not raise
+            self.assertEqual(self.signature(C),
+                            ((('a', ..., ..., "positional_or_keyword"),),
+                            ...))
+
+        with self.subTest('partialmethod'):
+            class C:
+                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"),),
+                            ...))
+
+    def test_signature_on_class_with_new(self):
+        with self.subTest('FunctionType'):
+            class C:
+                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
+                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
+                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:
+                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__ = 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(lambda cls, x, a: (x, a), 2)
+
+            self.assertEqual(C(1), (2, 1))
+            self.assertEqual(self.signature(C),
+                            ((('a', ..., ..., "positional_or_keyword"),),
+                            ...))
+
+        with self.subTest('BuiltinMethodType'):
+            class C:
+                __new__ = str.__subclasscheck__
+
+            self.assertEqual(C(), False)
+            # TODO: Support BuiltinMethodType
+            # self.assertEqual(self.signature(C), ((), ...))
+            self.assertRaises(ValueError, self.signature, C)
+
+        with self.subTest('MethodWrapperType'):
+            class C:
+                __new__ = type.__or__.__get__(int, type)
+
+            self.assertEqual(C(), C | int)
+            # TODO: Support MethodWrapperType
+            # self.assertEqual(self.signature(C), ((), ...))
+            self.assertRaises(ValueError, self.signature, C)
+
+        # TODO: Test ClassMethodDescriptorType
+
+        with self.subTest('MethodDescriptorType'):
+            class C:
+                __new__ = type.__dict__['__subclasscheck__']
+
+            self.assertEqual(C(C), True)
+            self.assertEqual(self.signature(C), self.signature(C.__subclasscheck__))
+
+        with self.subTest('WrapperDescriptorType'):
+            class C:
+                __new__ = type.__or__
+
+            self.assertEqual(C(int), C | int)
+            # TODO: Support WrapperDescriptorType
+            # self.assertEqual(self.signature(C), self.signature(C.__or__))
+            self.assertRaises(ValueError, self.signature, C)
+
     def test_signature_on_subclass(self):
         class A:
             def __new__(cls, a=1, *args, **kwargs):
@@ -3437,8 +3695,11 @@ class TestSignatureObject(unittest.TestCase):
         # Test meta-classes without user-defined __init__ or __new__
         class C(type): pass
         class D(C): pass
+        self.assertEqual(C('A', (), {}).__name__, 'A')
+        # TODO: Support type.
         with self.assertRaisesRegex(ValueError, "callable.*is not supported"):
             self.assertEqual(inspect.signature(C), None)
+        self.assertEqual(D('A', (), {}).__name__, 'A')
         with self.assertRaisesRegex(ValueError, "callable.*is not supported"):
             self.assertEqual(inspect.signature(D), None)
 
@@ -3488,6 +3749,103 @@ class TestSignatureObject(unittest.TestCase):
                          ((('a', ..., ..., "positional_or_keyword"),),
                           ...))
 
+        with self.subTest('classmethod'):
+            class C:
+                @classmethod
+                def __call__(cls, a):
+                    pass
+
+            self.assertEqual(self.signature(C()),
+                            ((('a', ..., ..., "positional_or_keyword"),),
+                            ...))
+
+        with self.subTest('staticmethod'):
+            class C:
+                @staticmethod
+                def __call__(a):
+                    pass
+
+            self.assertEqual(self.signature(C()),
+                            ((('a', ..., ..., "positional_or_keyword"),),
+                            ...))
+
+        with self.subTest('MethodType'):
+            class A:
+                def call(self, a):
+                    return a
+            class C:
+                __call__ = A().call
+
+            self.assertEqual(C()(1), 1)
+            self.assertEqual(self.signature(C()),
+                            ((('a', ..., ..., "positional_or_keyword"),),
+                            ...))
+
+        with self.subTest('partial'):
+            class C:
+                __call__ = functools.partial(lambda x, 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:
+                __call__ = functools.partialmethod(lambda self, x, a: (x, a), 2)
+
+            self.assertEqual(C()(1), (2, 1))
+            self.assertEqual(self.signature(C()),
+                            ((('a', ..., ..., "positional_or_keyword"),),
+                            ...))
+
+        with self.subTest('BuiltinMethodType'):
+            class C:
+                __call__ = ':'.join
+
+            self.assertEqual(C()(['a', 'bc']), 'a:bc')
+            self.assertEqual(self.signature(C()), self.signature(''.join))
+
+        with self.subTest('MethodWrapperType'):
+            class C:
+                __call__ = (2).__pow__
+
+            self.assertEqual(C()(3), 8)
+            self.assertEqual(self.signature(C()), self.signature((0).__pow__))
+
+        with self.subTest('ClassMethodDescriptorType'):
+            class C(dict):
+                __call__ = dict.__dict__['fromkeys']
+
+            res = C()([1, 2], 3)
+            self.assertEqual(res, {1: 3, 2: 3})
+            self.assertEqual(type(res), C)
+            self.assertEqual(self.signature(C()), self.signature(dict.fromkeys))
+
+        with self.subTest('MethodDescriptorType'):
+            class C(str):
+                __call__ = str.join
+
+            self.assertEqual(C(':')(['a', 'bc']), 'a:bc')
+            self.assertEqual(self.signature(C()), self.signature(''.join))
+
+        with self.subTest('WrapperDescriptorType'):
+            class C(int):
+                __call__ = int.__pow__
+
+            self.assertEqual(C(2)(3), 8)
+            self.assertEqual(self.signature(C()), self.signature((0).__pow__))
+
+        with self.subTest('MemberDescriptorType'):
+            class C:
+                __slots__ = '__call__'
+            c = C()
+            c.__call__ = lambda a: a
+            self.assertEqual(c(1), 1)
+            self.assertEqual(self.signature(c),
+                            ((('a', ..., ..., "positional_or_keyword"),),
+                            ...))
+
     def test_signature_on_wrapper(self):
         class Wrapper:
             def __call__(self, b):
diff --git a/Misc/NEWS.d/next/Library/2024-02-15-19-11-49.gh-issue-101293.898b8l.rst b/Misc/NEWS.d/next/Library/2024-02-15-19-11-49.gh-issue-101293.898b8l.rst
new file mode 100644
index 0000000..98365d2
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-02-15-19-11-49.gh-issue-101293.898b8l.rst
@@ -0,0 +1,4 @@
+Support callables with the ``__call__()`` method and types with
+``__new__()`` and ``__init__()`` methods set to class methods, static
+methods, bound methods, partial functions, and other types of methods and
+descriptors in :meth:`inspect.Signature.from_callable`.