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.
This commit is contained in:
Ivan Levkivskyi 2017-12-14 23:32:56 +01:00 committed by GitHub
parent 15a8728415
commit 2b5fd1e9ca
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GPG Key ID: 4AEE18F83AFDEB23
7 changed files with 492 additions and 5 deletions

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@ -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()

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@ -844,6 +844,68 @@ class ClassCreationTests(unittest.TestCase):
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 ClassCreationTests(unittest.TestCase):
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

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@ -60,10 +60,34 @@ del sys, _f, _g, _C, _c, # Not for export
# 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.

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@ -0,0 +1,2 @@
PEP 560: Add support for __mro_entries__ and __class_getitem__. Implemented
by Ivan Levkivskyi.

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@ -168,6 +168,21 @@ PyObject_GetItem(PyObject *o, PyObject *key)
"be integer, not '%.200s'", key);
}
if (PyType_Check(o)) {
PyObject *meth, *result, *stack[2] = {o, key};
_Py_IDENTIFIER(__class_getitem__);
meth = _PyObject_GetAttrId(o, &PyId___class_getitem__);
if (meth) {
result = _PyObject_FastCall(meth, stack, 2);
Py_DECREF(meth);
return result;
}
else if (!PyErr_ExceptionMatches(PyExc_AttributeError)) {
return NULL;
}
PyErr_Clear();
}
return type_error("'%.200s' object is not subscriptable", o);
}

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@ -2377,6 +2377,27 @@ type_new(PyTypeObject *metatype, PyObject *args, PyObject *kwds)
nbases = 1;
}
else {
_Py_IDENTIFIER(__mro_entries__);
for (i = 0; i < nbases; i++) {
tmp = PyTuple_GET_ITEM(bases, i);
if (PyType_Check(tmp)) {
continue;
}
tmp = _PyObject_GetAttrId(tmp, &PyId___mro_entries__);
if (tmp != NULL) {
PyErr_SetString(PyExc_TypeError,
"type() doesn't support MRO entry resolution; "
"use types.new_class()");
Py_DECREF(tmp);
return NULL;
}
else if (PyErr_ExceptionMatches(PyExc_AttributeError)) {
PyErr_Clear();
}
else {
return NULL;
}
}
/* Search the bases for the proper metatype to deal with this: */
winner = _PyType_CalculateMetaclass(metatype, bases);
if (winner == NULL) {

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@ -37,6 +37,7 @@ _Py_IDENTIFIER(__builtins__);
_Py_IDENTIFIER(__dict__);
_Py_IDENTIFIER(__prepare__);
_Py_IDENTIFIER(__round__);
_Py_IDENTIFIER(__mro_entries__);
_Py_IDENTIFIER(encoding);
_Py_IDENTIFIER(errors);
_Py_IDENTIFIER(fileno);
@ -49,12 +50,86 @@ _Py_IDENTIFIER(stderr);
#include "clinic/bltinmodule.c.h"
static PyObject*
update_bases(PyObject *bases, PyObject *const *args, int nargs)
{
int i, j;
PyObject *base, *meth, *new_base, *result, *new_bases = NULL;
PyObject *stack[1] = {bases};
assert(PyTuple_Check(bases));
for (i = 0; i < nargs; i++) {
base = args[i];
if (PyType_Check(base)) {
if (new_bases) {
/* If we already have made a replacement, then we append every normal base,
otherwise just skip it. */
if (PyList_Append(new_bases, base) < 0) {
goto error;
}
}
continue;
}
meth = _PyObject_GetAttrId(base, &PyId___mro_entries__);
if (!meth) {
if (!PyErr_ExceptionMatches(PyExc_AttributeError)) {
goto error;
}
PyErr_Clear();
if (new_bases) {
if (PyList_Append(new_bases, base) < 0) {
goto error;
}
}
continue;
}
new_base = _PyObject_FastCall(meth, stack, 1);
Py_DECREF(meth);
if (!new_base) {
goto error;
}
if (!PyTuple_Check(new_base)) {
PyErr_SetString(PyExc_TypeError,
"__mro_entries__ must return a tuple");
Py_DECREF(new_base);
goto error;
}
if (!new_bases) {
/* If this is a first successful replacement, create new_bases list and
copy previously encountered bases. */
if (!(new_bases = PyList_New(i))) {
goto error;
}
for (j = 0; j < i; j++) {
base = args[j];
PyList_SET_ITEM(new_bases, j, base);
Py_INCREF(base);
}
}
j = PyList_GET_SIZE(new_bases);
if (PyList_SetSlice(new_bases, j, j, new_base) < 0) {
goto error;
}
Py_DECREF(new_base);
}
if (!new_bases) {
return bases;
}
result = PyList_AsTuple(new_bases);
Py_DECREF(new_bases);
return result;
error:
Py_XDECREF(new_bases);
return NULL;
}
/* AC: cannot convert yet, waiting for *args support */
static PyObject *
builtin___build_class__(PyObject *self, PyObject **args, Py_ssize_t nargs,
PyObject *kwnames)
{
PyObject *func, *name, *bases, *mkw, *meta, *winner, *prep, *ns;
PyObject *func, *name, *bases, *mkw, *meta, *winner, *prep, *ns, *orig_bases;
PyObject *cls = NULL, *cell = NULL;
int isclass = 0; /* initialize to prevent gcc warning */
@ -75,10 +150,16 @@ builtin___build_class__(PyObject *self, PyObject **args, Py_ssize_t nargs,
"__build_class__: name is not a string");
return NULL;
}
bases = _PyStack_AsTupleSlice(args, nargs, 2, nargs);
if (bases == NULL)
orig_bases = _PyStack_AsTupleSlice(args, nargs, 2, nargs);
if (orig_bases == NULL)
return NULL;
bases = update_bases(orig_bases, args + 2, nargs - 2);
if (bases == NULL) {
Py_DECREF(orig_bases);
return NULL;
}
if (kwnames == NULL) {
meta = NULL;
mkw = NULL;
@ -171,6 +252,11 @@ builtin___build_class__(PyObject *self, PyObject **args, Py_ssize_t nargs,
NULL, 0, NULL, 0, NULL, 0, NULL,
PyFunction_GET_CLOSURE(func));
if (cell != NULL) {
if (bases != orig_bases) {
if (PyMapping_SetItemString(ns, "__orig_bases__", orig_bases) < 0) {
goto error;
}
}
PyObject *margs[3] = {name, bases, ns};
cls = _PyObject_FastCallDict(meta, margs, 3, mkw);
if (cls != NULL && PyType_Check(cls) && PyCell_Check(cell)) {
@ -209,6 +295,9 @@ error:
Py_DECREF(meta);
Py_XDECREF(mkw);
Py_DECREF(bases);
if (bases != orig_bases) {
Py_DECREF(orig_bases);
}
return cls;
}