bpo-32226: Implementation of PEP 560 (core components) (#4732)
This part of the PEP implementation adds support for
__mro_entries__ and __class_getitem__ by updating
__build_class__ and PyObject_GetItem.
diff --git a/Lib/test/test_genericclass.py b/Lib/test/test_genericclass.py
new file mode 100644
index 0000000..214527b
--- /dev/null
+++ 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
index 28133a3..47488a6 100644
--- a/Lib/test/test_types.py
+++ b/Lib/test/test_types.py
@@ -844,6 +844,68 @@
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 @@
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
index 336918f..c5976f3 100644
--- a/Lib/types.py
+++ b/Lib/types.py
@@ -60,10 +60,34 @@
# 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.