python · ilevkivskyi · Dec 14, 2017 · Jul 19, 2017 · Jul 19, 2017 · Jul 20, 2017
diff --git a/Lib/test/test_genericclass.py b/Lib/test/test_genericclass.py
@@ -0,0 +1,252 @@
+import unittest
+
+
+class TestMROEntry(unittest.TestCase):
+    def test_mro_entry_signature(self):
+        tested = []
+        class B: ...
+        class C:
+            def __mro_entries__(self, *args, **kwargs):
+                tested.extend([args, kwargs])
+                return (C,)
+        c = C()
+        self.assertEqual(tested, [])
+        class D(B, c): ...
+        self.assertEqual(tested[0], ((B, c),))
+        self.assertEqual(tested[1], {})
+
+    def test_mro_entry(self):
+        tested = []
+        class A: ...
+        class B: ...
+        class C:
+            def __mro_entries__(self, bases):
+                tested.append(bases)
+                return (self.__class__,)
+        c = C()
+        self.assertEqual(tested, [])
+        class D(A, c, B): ...
+        self.assertEqual(tested[-1], (A, c, B))
+        self.assertEqual(D.__bases__, (A, C, B))
+        self.assertEqual(D.__orig_bases__, (A, c, B))
+        self.assertEqual(D.__mro__, (D, A, C, B, object))
+        d = D()
+        class E(d): ...
+        self.assertEqual(tested[-1], (d,))
+        self.assertEqual(E.__bases__, (D,))
+
+    def test_mro_entry_none(self):
+        tested = []
+        class A: ...
+        class B: ...
+        class C:
+            def __mro_entries__(self, bases):
+                tested.append(bases)
+                return ()
+        c = C()
+        self.assertEqual(tested, [])
+        class D(A, c, B): ...
+        self.assertEqual(tested[-1], (A, c, B))
+        self.assertEqual(D.__bases__, (A, B))
+        self.assertEqual(D.__orig_bases__, (A, c, B))
+        self.assertEqual(D.__mro__, (D, A, B, object))
+        class E(c): ...
+        self.assertEqual(tested[-1], (c,))
+        self.assertEqual(E.__bases__, (object,))
+        self.assertEqual(E.__orig_bases__, (c,))
+        self.assertEqual(E.__mro__, (E, object))
+
+    def test_mro_entry_with_builtins(self):
+        tested = []
+        class A: ...
+        class C:
+            def __mro_entries__(self, bases):
+                tested.append(bases)
+                return (dict,)
+        c = C()
+        self.assertEqual(tested, [])
+        class D(A, c): ...
+        self.assertEqual(tested[-1], (A, c))
+        self.assertEqual(D.__bases__, (A, dict))
+        self.assertEqual(D.__orig_bases__, (A, c))
+        self.assertEqual(D.__mro__, (D, A, dict, object))
+
+    def test_mro_entry_with_builtins_2(self):
+        tested = []
+        class C:
+            def __mro_entries__(self, bases):
+                tested.append(bases)
+                return (C,)
+        c = C()
+        self.assertEqual(tested, [])
+        class D(c, dict): ...
+        self.assertEqual(tested[-1], (c, dict))
+        self.assertEqual(D.__bases__, (C, dict))
+        self.assertEqual(D.__orig_bases__, (c, dict))
+        self.assertEqual(D.__mro__, (D, C, dict, object))
+
+    def test_mro_entry_errors(self):
+        class C_too_many:
+            def __mro_entries__(self, bases, something, other):
+                return ()
+        c = C_too_many()
+        with self.assertRaises(TypeError):
+            class D(c): ...
+        class C_too_few:
+            def __mro_entries__(self):
+                return ()
+        d = C_too_few()
+        with self.assertRaises(TypeError):
+            class D(d): ...
+
+    def test_mro_entry_errors_2(self):
+        class C_not_callable:
+            __mro_entries__ = "Surprise!"
+        c = C_not_callable()
+        with self.assertRaises(TypeError):
+            class D(c): ...
+        class C_not_tuple:
+            def __mro_entries__(self):
+                return object
+        c = C_not_tuple()
+        with self.assertRaises(TypeError):
+            class D(c): ...
+
+    def test_mro_entry_metaclass(self):
+        meta_args = []
+        class Meta(type):
+            def __new__(mcls, name, bases, ns):
+                meta_args.extend([mcls, name, bases, ns])
+                return super().__new__(mcls, name, bases, ns)
+        class A: ...
+        class C:
+            def __mro_entries__(self, bases):
+                return (A,)
+        c = C()
+        class D(c, metaclass=Meta):
+            x = 1
+        self.assertEqual(meta_args[0], Meta)
+        self.assertEqual(meta_args[1], 'D')
+        self.assertEqual(meta_args[2], (A,))
+        self.assertEqual(meta_args[3]['x'], 1)
+        self.assertEqual(D.__bases__, (A,))
+        self.assertEqual(D.__orig_bases__, (c,))
+        self.assertEqual(D.__mro__, (D, A, object))
+        self.assertEqual(D.__class__, Meta)
+
+    def test_mro_entry_type_call(self):
+        # Substitution should _not_ happen in direct type call
+        class C:
+            def __mro_entries__(self, bases):
+                return ()
+        c = C()
+        with self.assertRaisesRegex(TypeError,
+                                    "MRO entry resolution; "
+                                    "use types.new_class()"):
+            type('Bad', (c,), {})
+
+
+class TestClassGetitem(unittest.TestCase):
+    def test_class_getitem(self):
+        getitem_args = []
+        class C:
+            def __class_getitem__(*args, **kwargs):
+                getitem_args.extend([args, kwargs])
+                return None
+        C[int, str]
+        self.assertEqual(getitem_args[0], (C, (int, str)))
+        self.assertEqual(getitem_args[1], {})
+
+    def test_class_getitem(self):
+        class C:
+            def __class_getitem__(cls, item):
+                return f'C[{item.__name__}]'
+        self.assertEqual(C[int], 'C[int]')
+        self.assertEqual(C[C], 'C[C]')
+
+    def test_class_getitem_inheritance(self):
+        class C:
+            def __class_getitem__(cls, item):
+                return f'{cls.__name__}[{item.__name__}]'
+        class D(C): ...
+        self.assertEqual(D[int], 'D[int]')
+        self.assertEqual(D[D], 'D[D]')
+
+    def test_class_getitem_inheritance_2(self):
+        class C:
+            def __class_getitem__(cls, item):
+                return 'Should not see this'
+        class D(C):
+            def __class_getitem__(cls, item):
+                return f'{cls.__name__}[{item.__name__}]'
+        self.assertEqual(D[int], 'D[int]')
+        self.assertEqual(D[D], 'D[D]')
+
+    def test_class_getitem_patched(self):
+        class C:
+            def __init_subclass__(cls):
+                def __class_getitem__(cls, item):
+                    return f'{cls.__name__}[{item.__name__}]'
+                cls.__class_getitem__ = __class_getitem__
+        class D(C): ...
+        self.assertEqual(D[int], 'D[int]')
+        self.assertEqual(D[D], 'D[D]')
+
+    def test_class_getitem_with_builtins(self):
+        class A(dict):
+            called_with = None
+
+            def __class_getitem__(cls, item):
+                cls.called_with = item
+        class B(A):
+            pass
+        self.assertIs(B.called_with, None)
+        B[int]
+        self.assertIs(B.called_with, int)
+
+    def test_class_getitem_errors(self):
+        class C_too_few:
+            def __class_getitem__(cls):
+                return None
+        with self.assertRaises(TypeError):
+            C_too_few[int]
+        class C_too_many:
+            def __class_getitem__(cls, one, two):
+                return None
+        with self.assertRaises(TypeError):
+            C_too_many[int]
+
+    def test_class_getitem_errors_2(self):
+        class C:
+            def __class_getitem__(cls, item):
+                return None
+        with self.assertRaises(TypeError):
+            C()[int]
+        class E: ...
+        e = E()
+        e.__class_getitem__ = lambda cls, item: 'This will not work'
+        with self.assertRaises(TypeError):
+            e[int]
+        class C_not_callable:
+            __class_getitem__ = "Surprise!"
+        with self.assertRaises(TypeError):
+            C_not_callable[int]
+
+    def test_class_getitem_metaclass(self):
+        class Meta(type):
+            def __class_getitem__(cls, item):
+                return f'{cls.__name__}[{item.__name__}]'
+        self.assertEqual(Meta[int], 'Meta[int]')
+
+    def test_class_getitem_metaclass_2(self):
+        class Meta(type):
+            def __getitem__(cls, item):
+                return 'from metaclass'
+        class C(metaclass=Meta):
+            def __class_getitem__(cls, item):
+                return 'from __class_getitem__'
+        self.assertEqual(C[int], 'from metaclass')
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/Lib/test/test_types.py b/Lib/test/test_types.py
@@ -844,6 +844,68 @@ def func(ns):
         self.assertEqual(C.y, 1)
         self.assertEqual(C.z, 2)
 
+    def test_new_class_with_mro_entry(self):
+        class A: pass
+        class C:
+            def __mro_entries__(self, bases):
+                return (A,)
+        c = C()
+        D = types.new_class('D', (c,), {})
+        self.assertEqual(D.__bases__, (A,))
+        self.assertEqual(D.__orig_bases__, (c,))
+        self.assertEqual(D.__mro__, (D, A, object))
+
+    def test_new_class_with_mro_entry_none(self):
+        class A: pass
+        class B: pass
+        class C:
+            def __mro_entries__(self, bases):
+                return ()
+        c = C()
+        D = types.new_class('D', (A, c, B), {})
+        self.assertEqual(D.__bases__, (A, B))
+        self.assertEqual(D.__orig_bases__, (A, c, B))
+        self.assertEqual(D.__mro__, (D, A, B, object))
+
+    def test_new_class_with_mro_entry_error(self):
+        class A: pass
+        class C:
+            def __mro_entries__(self, bases):
+                return A
+        c = C()
+        with self.assertRaises(TypeError):
+            types.new_class('D', (c,), {})
+
+    def test_new_class_with_mro_entry_multiple(self):
+        class A1: pass
+        class A2: pass
+        class B1: pass
+        class B2: pass
+        class A:
+            def __mro_entries__(self, bases):
+                return (A1, A2)
+        class B:
+            def __mro_entries__(self, bases):
+                return (B1, B2)
+        D = types.new_class('D', (A(), B()), {})
+        self.assertEqual(D.__bases__, (A1, A2, B1, B2))
+
+    def test_new_class_with_mro_entry_multiple_2(self):
+        class A1: pass
+        class A2: pass
+        class A3: pass
+        class B1: pass
+        class B2: pass
+        class A:
+            def __mro_entries__(self, bases):
+                return (A1, A2, A3)
+        class B:
+            def __mro_entries__(self, bases):
+                return (B1, B2)
+        class C: pass
+        D = types.new_class('D', (A(), C, B()), {})
+        self.assertEqual(D.__bases__, (A1, A2, A3, C, B1, B2))
+
     # Many of the following tests are derived from test_descr.py
     def test_prepare_class(self):
         # Basic test of metaclass derivation
@@ -886,6 +948,28 @@ def __prepare__(*args):
             class Bar(metaclass=BadMeta()):
                 pass
 
+    def test_resolve_bases(self):
+        class A: pass
+        class B: pass
+        class C:
+            def __mro_entries__(self, bases):
+                if A in bases:
+                    return ()
+                return (A,)
+        c = C()
+        self.assertEqual(types.resolve_bases(()), ())
+        self.assertEqual(types.resolve_bases((c,)), (A,))
+        self.assertEqual(types.resolve_bases((C,)), (C,))
+        self.assertEqual(types.resolve_bases((A, C)), (A, C))
+        self.assertEqual(types.resolve_bases((c, A)), (A,))
+        self.assertEqual(types.resolve_bases((A, c)), (A,))
+        x = (A,)
+        y = (C,)
+        z = (A, C)
+        t = (A, C, B)
+        for bases in [x, y, z, t]:
+            self.assertIs(types.resolve_bases(bases), bases)
+
     def test_metaclass_derivation(self):
         # issue1294232: correct metaclass calculation
         new_calls = []  # to check the order of __new__ calls

diff --git a/Lib/types.py b/Lib/types.py
@@ -60,10 +60,34 @@ def _m(self): pass
 # Provide a PEP 3115 compliant mechanism for class creation
 def new_class(name, bases=(), kwds=None, exec_body=None):
     """Create a class object dynamically using the appropriate metaclass."""
-    meta, ns, kwds = prepare_class(name, bases, kwds)
+    resolved_bases = resolve_bases(bases)
+    meta, ns, kwds = prepare_class(name, resolved_bases, kwds)
     if exec_body is not None:
         exec_body(ns)
-    return meta(name, bases, ns, **kwds)
+    if resolved_bases is not bases:
+        ns['__orig_bases__'] = bases
+    return meta(name, resolved_bases, ns, **kwds)
+
+def resolve_bases(bases):
+    """Resolve MRO entries dynamically as specified by PEP 560."""
+    new_bases = list(bases)
+    updated = False
+    shift = 0
+    for i, base in enumerate(bases):
+        if isinstance(base, type):
+            continue
+        if not hasattr(base, "__mro_entries__"):
+            continue
+        new_base = base.__mro_entries__(bases)
+        updated = True
+        if not isinstance(new_base, tuple):
+            raise TypeError("__mro_entries__ must return a tuple")
+        else:
+            new_bases[i+shift:i+shift+1] = new_base
+            shift += len(new_base) - 1
+    if not updated:
+        return bases
+    return tuple(new_bases)
 
 def prepare_class(name, bases=(), kwds=None):
     """Call the __prepare__ method of the appropriate metaclass.

diff --git a/Misc/NEWS.d/next/Core and Builtins/2017-12-05-21-42-58.bpo-32226.G8fqb6.rst b/Misc/NEWS.d/next/Core and Builtins/2017-12-05-21-42-58.bpo-32226.G8fqb6.rst
@@ -0,0 +1,2 @@
+PEP 560: Add support for __mro_entries__ and __class_getitem__. Implemented
+by Ivan Levkivskyi.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		PEP 560: Add support for __mro_entries__ and __class_getitem__. Implemented
		by Ivan Levkivskyi.