Issue #27366: Implement PEP 487

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

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()