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Commit1f1a34c

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bpo-32379: Faster MRO computation for single inheritance (#4932)
*bpo-32379: Faster MRO computation for single inheritance
1 parent776407f commit1f1a34c

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3 files changed

+43
-4
lines changed

3 files changed

+43
-4
lines changed

‎Lib/test/test_descr.py‎

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1783,6 +1783,12 @@ class C(A):
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deff(self):return"C"
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classD(B,C):
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pass
1786+
self.assertEqual(A.mro(), [A,object])
1787+
self.assertEqual(A.__mro__, (A,object))
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self.assertEqual(B.mro(), [B,A,object])
1789+
self.assertEqual(B.__mro__, (B,A,object))
1790+
self.assertEqual(C.mro(), [C,A,object])
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self.assertEqual(C.__mro__, (C,A,object))
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self.assertEqual(D.mro(), [D,B,C,A,object])
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self.assertEqual(D.__mro__, (D,B,C,A,object))
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self.assertEqual(D().f(),"C")
Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1 @@
1+
Make MRO computation faster when a class inherits from a single base.

‎Objects/typeobject.c‎

Lines changed: 36 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1761,6 +1761,36 @@ mro_implementation(PyTypeObject *type)
17611761
returnNULL;
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}
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1764+
bases=type->tp_bases;
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n=PyTuple_GET_SIZE(bases);
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if (n==1) {
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/* Fast path: if there is a single base, constructing the MRO
1768+
* is trivial.
1769+
*/
1770+
PyTypeObject*base= (PyTypeObject*)PyTuple_GET_ITEM(bases,0);
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Py_ssize_tk;
1772+
1773+
if (base->tp_mro==NULL) {
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PyErr_Format(PyExc_TypeError,
1775+
"Cannot extend an incomplete type '%.100s'",
1776+
base->tp_name);
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returnNULL;
1778+
}
1779+
k=PyTuple_GET_SIZE(base->tp_mro);
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result=PyTuple_New(k+1);
1781+
if (result==NULL) {
1782+
returnNULL;
1783+
}
1784+
Py_INCREF(type);
1785+
PyTuple_SET_ITEM(result,0, (PyObject*)type);
1786+
for (i=0;i<k;i++) {
1787+
PyObject*cls=PyTuple_GET_ITEM(base->tp_mro,i);
1788+
Py_INCREF(cls);
1789+
PyTuple_SET_ITEM(result,i+1,cls);
1790+
}
1791+
returnresult;
1792+
}
1793+
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/* Find a superclass linearization that honors the constraints
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of the explicit lists of bases and the constraints implied by
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each base class.
@@ -1770,9 +1800,6 @@ mro_implementation(PyTypeObject *type)
17701800
to_merge is the declared list of bases.
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*/
17721802

1773-
bases=type->tp_bases;
1774-
n=PyTuple_GET_SIZE(bases);
1775-
17761803
to_merge=PyList_New(n+1);
17771804
if (to_merge==NULL)
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returnNULL;
@@ -1830,7 +1857,12 @@ static PyObject *
18301857
type_mro_impl(PyTypeObject*self)
18311858
/*[clinic end generated code: output=bffc4a39b5b57027 input=28414f4e156db28d]*/
18321859
{
1833-
returnmro_implementation(self);
1860+
PyObject*seq;
1861+
seq=mro_implementation(self);
1862+
if (seq!=NULL&& !PyList_Check(seq)) {
1863+
Py_SETREF(seq,PySequence_List(seq));
1864+
}
1865+
returnseq;
18341866
}
18351867

18361868
staticint

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