Issue #27366: Implement PEP 487

- __init_subclass__ called when new subclasses defined
- __set_name__ called when descriptors are part of a
  class definition

4 files changed, 252 insertions, 16 deletions

diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index 8cc1b00..acc4f9c 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -1699,21 +1699,11 @@ class TestType(unittest.TestCase):
         self.assertEqual(x.spam(), 'spam42')
         self.assertEqual(x.to_bytes(2, 'little'), b'\x2a\x00')
 
-    def test_type_new_keywords(self):
-        class B:
-            def ham(self):
-                return 'ham%d' % self
-        C = type.__new__(type,
-                         name='C',
-                         bases=(B, int),
-                         dict={'spam': lambda self: 'spam%s' % self})
-        self.assertEqual(C.__name__, 'C')
-        self.assertEqual(C.__qualname__, 'C')
-        self.assertEqual(C.__module__, __name__)
-        self.assertEqual(C.__bases__, (B, int))
-        self.assertIs(C.__base__, int)
-        self.assertIn('spam', C.__dict__)
-        self.assertNotIn('ham', C.__dict__)
+    def test_type_nokwargs(self):
+        with self.assertRaises(TypeError):
+            type('a', (), {}, x=5)
+        with self.assertRaises(TypeError):
+            type('a', (), dict={})
 
     def test_type_name(self):
         for name in 'A', '\xc4', '\U0001f40d', 'B.A', '42', '':
diff --git a/Lib/test/test_descrtut.py b/Lib/test/test_descrtut.py
index 506d1ab..b84d644 100644
--- a/Lib/test/test_descrtut.py
+++ b/Lib/test/test_descrtut.py
@@ -182,6 +182,7 @@ You can get the information from the list type:
      '__iadd__',
      '__imul__',
      '__init__',
+     '__init_subclass__',
      '__iter__',
      '__le__',
      '__len__',
diff --git a/Lib/test/test_pydoc.py b/Lib/test/test_pydoc.py
index 889ce59..4998597 100644
--- a/Lib/test/test_pydoc.py
+++ b/Lib/test/test_pydoc.py
@@ -638,8 +638,9 @@ class PydocDocTest(unittest.TestCase):
         del expected['__doc__']
         del expected['__class__']
         # inspect resolves descriptors on type into methods, but vars doesn't,
-        # so we need to update __subclasshook__.
+        # so we need to update __subclasshook__ and __init_subclass__.
         expected['__subclasshook__'] = TestClass.__subclasshook__
+        expected['__init_subclass__'] = TestClass.__init_subclass__
 
         methods = pydoc.allmethods(TestClass)
         self.assertDictEqual(methods, expected)
diff --git a/Lib/test/test_subclassinit.py b/Lib/test/test_subclassinit.py
new file mode 100644
index 0000000..eb5ed70
--- /dev/null
+++ b/Lib/test/test_subclassinit.py
@@ -0,0 +1,244 @@
+from unittest import TestCase, main
+import sys
+import types
+
+
+class Test(TestCase):
+    def test_init_subclass(self):
+        class A(object):
+            initialized = False
+
+            def __init_subclass__(cls):
+                super().__init_subclass__()
+                cls.initialized = True
+
+        class B(A):
+            pass
+
+        self.assertFalse(A.initialized)
+        self.assertTrue(B.initialized)
+
+    def test_init_subclass_dict(self):
+        class A(dict, object):
+            initialized = False
+
+            def __init_subclass__(cls):
+                super().__init_subclass__()
+                cls.initialized = True
+
+        class B(A):
+            pass
+
+        self.assertFalse(A.initialized)
+        self.assertTrue(B.initialized)
+
+    def test_init_subclass_kwargs(self):
+        class A(object):
+            def __init_subclass__(cls, **kwargs):
+                cls.kwargs = kwargs
+
+        class B(A, x=3):
+            pass
+
+        self.assertEqual(B.kwargs, dict(x=3))
+
+    def test_init_subclass_error(self):
+        class A(object):
+            def __init_subclass__(cls):
+                raise RuntimeError
+
+        with self.assertRaises(RuntimeError):
+            class B(A):
+                pass
+
+    def test_init_subclass_wrong(self):
+        class A(object):
+            def __init_subclass__(cls, whatever):
+                pass
+
+        with self.assertRaises(TypeError):
+            class B(A):
+                pass
+
+    def test_init_subclass_skipped(self):
+        class BaseWithInit(object):
+            def __init_subclass__(cls, **kwargs):
+                super().__init_subclass__(**kwargs)
+                cls.initialized = cls
+
+        class BaseWithoutInit(BaseWithInit):
+            pass
+
+        class A(BaseWithoutInit):
+            pass
+
+        self.assertIs(A.initialized, A)
+        self.assertIs(BaseWithoutInit.initialized, BaseWithoutInit)
+
+    def test_init_subclass_diamond(self):
+        class Base(object):
+            def __init_subclass__(cls, **kwargs):
+                super().__init_subclass__(**kwargs)
+                cls.calls = []
+
+        class Left(Base):
+            pass
+
+        class Middle(object):
+            def __init_subclass__(cls, middle, **kwargs):
+                super().__init_subclass__(**kwargs)
+                cls.calls += [middle]
+
+        class Right(Base):
+            def __init_subclass__(cls, right="right", **kwargs):
+                super().__init_subclass__(**kwargs)
+                cls.calls += [right]
+
+        class A(Left, Middle, Right, middle="middle"):
+            pass
+
+        self.assertEqual(A.calls, ["right", "middle"])
+        self.assertEqual(Left.calls, [])
+        self.assertEqual(Right.calls, [])
+
+    def test_set_name(self):
+        class Descriptor:
+            def __set_name__(self, owner, name):
+                self.owner = owner
+                self.name = name
+
+        class A(object):
+            d = Descriptor()
+
+        self.assertEqual(A.d.name, "d")
+        self.assertIs(A.d.owner, A)
+
+    def test_set_name_metaclass(self):
+        class Meta(type):
+            def __new__(cls, name, bases, ns):
+                ret = super().__new__(cls, name, bases, ns)
+                self.assertEqual(ret.d.name, "d")
+                self.assertIs(ret.d.owner, ret)
+                return 0
+
+        class Descriptor(object):
+            def __set_name__(self, owner, name):
+                self.owner = owner
+                self.name = name
+
+        class A(object, metaclass=Meta):
+            d = Descriptor()
+        self.assertEqual(A, 0)
+
+    def test_set_name_error(self):
+        class Descriptor:
+            def __set_name__(self, owner, name):
+                raise RuntimeError
+
+        with self.assertRaises(RuntimeError):
+            class A(object):
+                d = Descriptor()
+
+    def test_set_name_wrong(self):
+        class Descriptor:
+            def __set_name__(self):
+                pass
+
+        with self.assertRaises(TypeError):
+            class A(object):
+                d = Descriptor()
+
+    def test_set_name_init_subclass(self):
+        class Descriptor:
+            def __set_name__(self, owner, name):
+                self.owner = owner
+                self.name = name
+
+        class Meta(type):
+            def __new__(cls, name, bases, ns):
+                self = super().__new__(cls, name, bases, ns)
+                self.meta_owner = self.owner
+                self.meta_name = self.name
+                return self
+
+        class A(object):
+            def __init_subclass__(cls):
+                cls.owner = cls.d.owner
+                cls.name = cls.d.name
+
+        class B(A, metaclass=Meta):
+            d = Descriptor()
+
+        self.assertIs(B.owner, B)
+        self.assertEqual(B.name, 'd')
+        self.assertIs(B.meta_owner, B)
+        self.assertEqual(B.name, 'd')
+
+    def test_errors(self):
+        class MyMeta(type):
+            pass
+
+        with self.assertRaises(TypeError):
+            class MyClass(object, metaclass=MyMeta, otherarg=1):
+                pass
+
+        with self.assertRaises(TypeError):
+            types.new_class("MyClass", (object,),
+                            dict(metaclass=MyMeta, otherarg=1))
+        types.prepare_class("MyClass", (object,),
+                            dict(metaclass=MyMeta, otherarg=1))
+
+        class MyMeta(type):
+            def __init__(self, name, bases, namespace, otherarg):
+                super().__init__(name, bases, namespace)
+
+        with self.assertRaises(TypeError):
+            class MyClass(object, metaclass=MyMeta, otherarg=1):
+                pass
+
+        class MyMeta(type):
+            def __new__(cls, name, bases, namespace, otherarg):
+                return super().__new__(cls, name, bases, namespace)
+
+            def __init__(self, name, bases, namespace, otherarg):
+                super().__init__(name, bases, namespace)
+                self.otherarg = otherarg
+
+        class MyClass(object, metaclass=MyMeta, otherarg=1):
+            pass
+
+        self.assertEqual(MyClass.otherarg, 1)
+
+    def test_errors_changed_pep487(self):
+        # These tests failed before Python 3.6, PEP 487
+        class MyMeta(type):
+            def __new__(cls, name, bases, namespace):
+                return super().__new__(cls, name=name, bases=bases,
+                                       dict=namespace)
+
+        with self.assertRaises(TypeError):
+            class MyClass(object, metaclass=MyMeta):
+                pass
+
+        class MyMeta(type):
+            def __new__(cls, name, bases, namespace, otherarg):
+                self = super().__new__(cls, name, bases, namespace)
+                self.otherarg = otherarg
+                return self
+
+        class MyClass(object, metaclass=MyMeta, otherarg=1):
+            pass
+
+        self.assertEqual(MyClass.otherarg, 1)
+
+    def test_type(self):
+        t = type('NewClass', (object,), {})
+        self.assertIsInstance(t, type)
+        self.assertEqual(t.__name__, 'NewClass')
+
+        with self.assertRaises(TypeError):
+            type(name='NewClass', bases=(object,), dict={})
+
+
+if __name__ == "__main__":
+    main()