From 82550d5b8654cee55357cef303038effa4e0448a Mon Sep 17 00:00:00 2001
From: Tim Peters <tim.peters@gmail.com>
Date: Tue, 8 Apr 2003 19:02:34 +0000
Subject: Added private API function _PyInstance_Lookup().  This is part of
 backporting fixes so that garbage collection doesn't have to trigger
 execution of arbitrary Python code just to figure out whether an object has a
 __del__ method.

---
 Include/classobject.h | 12 ++++++++++++
 Objects/classobject.c | 37 +++++++++++++++++++++++++++++--------
 2 files changed, 41 insertions(+), 8 deletions(-)

diff --git a/Include/classobject.h b/Include/classobject.h
index c79f4a2..16af37b 100644
--- a/Include/classobject.h
+++ b/Include/classobject.h
@@ -51,6 +51,18 @@ extern DL_IMPORT(PyObject *) PyMethod_Function(PyObject *);
 extern DL_IMPORT(PyObject *) PyMethod_Self(PyObject *);
 extern DL_IMPORT(PyObject *) PyMethod_Class(PyObject *);
 
+/* Look up attribute with name (a string) on instance object pinst, using
+ * only the instance and base class dicts.  If a descriptor is found in
+ * a class dict, the descriptor is returned without calling it.
+ * Returns NULL if nothing found, else a borrowed reference to the
+ * value associated with name in the dict in which name was found.
+ * The point of this routine is that it never calls arbitrary Python
+ * code, so is always "safe":  all it does is dict lookups.  The function
+ * can't fail, never sets an exception, and NULL is not an error (it just
+ * means "not found").
+ */
+PyAPI_FUNC(PyObject *) _PyInstance_Lookup(PyObject *pinst, PyObject *name);
+
 /* Macros for direct access to these values. Type checks are *not*
    done, so use with care. */
 #define PyMethod_GET_FUNCTION(meth) \
diff --git a/Objects/classobject.c b/Objects/classobject.c
index c1c4a3e..90f169e 100644
--- a/Objects/classobject.c
+++ b/Objects/classobject.c
@@ -729,6 +729,27 @@ instance_getattr(register PyInstanceObject *inst, PyObject *name)
 	return res;
 }
 
+/* See classobject.h comments:  this only does dict lookups, and is always
+ * safe to call.
+ */
+PyObject *
+_PyInstance_Lookup(PyObject *pinst, PyObject *name)
+{
+	PyObject *v;
+	PyClassObject *class;
+	PyInstanceObject *inst;	/* pinst cast to the right type */
+
+	assert(PyInstance_Check(pinst));
+	inst = (PyInstanceObject *)pinst;
+
+	assert(PyString_Check(name));
+
+ 	v = PyDict_GetItem(inst->in_dict, name);
+	if (v == NULL)
+		v = class_lookup(inst->in_class, name, &class);
+	return v;
+}
+
 static int
 instance_setattr1(PyInstanceObject *inst, PyObject *name, PyObject *v)
 {
@@ -1056,7 +1077,7 @@ sliceobj_from_intint(int i, int j)
 	start = PyInt_FromLong((long)i);
 	if (!start)
 		return NULL;
-	
+
 	end = PyInt_FromLong((long)j);
 	if (!end) {
 		Py_DECREF(start);
@@ -1088,9 +1109,9 @@ instance_slice(PyInstanceObject *inst, int i, int j)
 		if (func == NULL)
 			return NULL;
 		arg = Py_BuildValue("(N)", sliceobj_from_intint(i, j));
-	} else 
+	} else
 		arg = Py_BuildValue("(ii)", i, j);
-		
+
 	if (arg == NULL) {
 		Py_DECREF(func);
 		return NULL;
@@ -1219,7 +1240,7 @@ instance_contains(PyInstanceObject *inst, PyObject *member)
 		res = PyEval_CallObject(func, arg);
 		Py_DECREF(func);
 		Py_DECREF(arg);
-		if(res == NULL) 
+		if(res == NULL)
 			return -1;
 		ret = PyObject_IsTrue(res);
 		Py_DECREF(res);
@@ -1292,7 +1313,7 @@ static PyObject *coerce_obj;
 
 /* Try one half of a binary operator involving a class instance. */
 static PyObject *
-half_binop(PyObject *v, PyObject *w, char *opname, binaryfunc thisfunc, 
+half_binop(PyObject *v, PyObject *w, char *opname, binaryfunc thisfunc,
 		int swapped)
 {
 	PyObject *args;
@@ -1300,7 +1321,7 @@ half_binop(PyObject *v, PyObject *w, char *opname, binaryfunc thisfunc,
 	PyObject *coerced = NULL;
 	PyObject *v1;
 	PyObject *result;
-	
+
 	if (!PyInstance_Check(v)) {
 		Py_INCREF(Py_NotImplemented);
 		return Py_NotImplemented;
@@ -1654,7 +1675,7 @@ bin_power(PyObject *v, PyObject *w)
 /* This version is for ternary calls only (z != None) */
 static PyObject *
 instance_pow(PyObject *v, PyObject *w, PyObject *z)
-{	
+{
 	if (z == Py_None) {
 		return do_binop(v, w, "__pow__", "__rpow__", bin_power);
 	}
@@ -1723,7 +1744,7 @@ instance_ipow(PyObject *v, PyObject *w, PyObject *z)
 #define NAME_OPS 6
 static PyObject **name_op = NULL;
 
-static int 
+static int
 init_name_op(void)
 {
 	int i;
-- 
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