bpo-36048: Use __index__() instead of __int__() for implicit conversion if available. (GH-11952)

Deprecate using the __int__() method in implicit conversions of Python
numbers to C integers.

2 files changed, 82 insertions, 14 deletions

diff --git a/Objects/abstract.c b/Objects/abstract.c
index 0565ba3..68d06ed 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -759,8 +759,9 @@ int
 PyNumber_Check(PyObject *o)
 {
     return o && o->ob_type->tp_as_number &&
-           (o->ob_type->tp_as_number->nb_int ||
-        o->ob_type->tp_as_number->nb_float);
+           (o->ob_type->tp_as_number->nb_index ||
+            o->ob_type->tp_as_number->nb_int ||
+            o->ob_type->tp_as_number->nb_float);
 }
 
 /* Binary operators */
@@ -1366,7 +1367,7 @@ PyNumber_Long(PyObject *o)
     }
     m = o->ob_type->tp_as_number;
     if (m && m->nb_int) { /* This should include subclasses of int */
-        result = (PyObject *)_PyLong_FromNbInt(o);
+        result = _PyLong_FromNbInt(o);
         if (result != NULL && !PyLong_CheckExact(result)) {
             Py_SETREF(result, _PyLong_Copy((PyLongObject *)result));
         }
@@ -1386,7 +1387,7 @@ PyNumber_Long(PyObject *o)
         /* __trunc__ is specified to return an Integral type,
            but int() needs to return an int. */
         m = result->ob_type->tp_as_number;
-        if (m == NULL || m->nb_int == NULL) {
+        if (m == NULL || (m->nb_index == NULL && m->nb_int == NULL)) {
             PyErr_Format(
                 PyExc_TypeError,
                 "__trunc__ returned non-Integral (type %.200s)",
@@ -1394,7 +1395,7 @@ PyNumber_Long(PyObject *o)
             Py_DECREF(result);
             return NULL;
         }
-        Py_SETREF(result, (PyObject *)_PyLong_FromNbInt(result));
+        Py_SETREF(result, _PyLong_FromNbIndexOrNbInt(result));
         if (result != NULL && !PyLong_CheckExact(result)) {
             Py_SETREF(result, _PyLong_Copy((PyLongObject *)result));
         }
diff --git a/Objects/longobject.c b/Objects/longobject.c
index d7b01ce..1e3445c 100644
--- a/Objects/longobject.c
+++ b/Objects/longobject.c
@@ -140,7 +140,7 @@ long_normalize(PyLongObject *v)
    nb_int slot is not available or the result of the call to nb_int
    returns something not of type int.
 */
-PyLongObject *
+PyObject *
 _PyLong_FromNbInt(PyObject *integral)
 {
     PyNumberMethods *nb;
@@ -149,7 +149,7 @@ _PyLong_FromNbInt(PyObject *integral)
     /* Fast path for the case that we already have an int. */
     if (PyLong_CheckExact(integral)) {
         Py_INCREF(integral);
-        return (PyLongObject *)integral;
+        return integral;
     }
 
     nb = Py_TYPE(integral)->tp_as_number;
@@ -164,7 +164,7 @@ _PyLong_FromNbInt(PyObject *integral)
        of exact type int. */
     result = nb->nb_int(integral);
     if (!result || PyLong_CheckExact(result))
-        return (PyLongObject *)result;
+        return result;
     if (!PyLong_Check(result)) {
         PyErr_Format(PyExc_TypeError,
                      "__int__ returned non-int (type %.200s)",
@@ -181,7 +181,74 @@ _PyLong_FromNbInt(PyObject *integral)
         Py_DECREF(result);
         return NULL;
     }
-    return (PyLongObject *)result;
+    return result;
+}
+
+/* Convert the given object to a PyLongObject using the nb_index or
+   nb_int slots, if available (the latter is deprecated).
+   Raise TypeError if either nb_index and nb_int slots are not
+   available or the result of the call to nb_index or nb_int
+   returns something not of type int.
+   Should be replaced with PyNumber_Index after the end of the
+   deprecation period.
+*/
+PyObject *
+_PyLong_FromNbIndexOrNbInt(PyObject *integral)
+{
+    PyNumberMethods *nb;
+    PyObject *result;
+
+    /* Fast path for the case that we already have an int. */
+    if (PyLong_CheckExact(integral)) {
+        Py_INCREF(integral);
+        return integral;
+    }
+
+    nb = Py_TYPE(integral)->tp_as_number;
+    if (nb == NULL || (nb->nb_index == NULL && nb->nb_int == NULL)) {
+        PyErr_Format(PyExc_TypeError,
+                     "an integer is required (got type %.200s)",
+                     Py_TYPE(integral)->tp_name);
+        return NULL;
+    }
+
+    if (nb->nb_index) {
+    /* Convert using the nb_index slot, which should return something
+       of exact type int. */
+        result = nb->nb_index(integral);
+        if (!result || PyLong_CheckExact(result))
+            return result;
+        if (!PyLong_Check(result)) {
+            PyErr_Format(PyExc_TypeError,
+                         "__index__ returned non-int (type %.200s)",
+                         result->ob_type->tp_name);
+            Py_DECREF(result);
+            return NULL;
+        }
+        /* Issue #17576: warn if 'result' not of exact type int. */
+        if (PyErr_WarnFormat(PyExc_DeprecationWarning, 1,
+                "__index__ returned non-int (type %.200s).  "
+                "The ability to return an instance of a strict subclass of int "
+                "is deprecated, and may be removed in a future version of Python.",
+                result->ob_type->tp_name))
+        {
+            Py_DECREF(result);
+            return NULL;
+        }
+        return result;
+    }
+
+    result = _PyLong_FromNbInt(integral);
+    if (result && PyErr_WarnFormat(PyExc_DeprecationWarning, 1,
+            "an integer is required (got type %.200s).  "
+            "Implicit conversion to integers using __int__ is deprecated, "
+            "and may be removed in a future version of Python.",
+            Py_TYPE(integral)->tp_name))
+    {
+        Py_DECREF(result);
+        return NULL;
+    }
+    return result;
 }
 
 
@@ -420,7 +487,7 @@ PyLong_AsLongAndOverflow(PyObject *vv, int *overflow)
         v = (PyLongObject *)vv;
     }
     else {
-        v = _PyLong_FromNbInt(vv);
+        v = (PyLongObject *)_PyLong_FromNbIndexOrNbInt(vv);
         if (v == NULL)
             return -1;
         do_decref = 1;
@@ -700,7 +767,7 @@ PyLong_AsUnsignedLongMask(PyObject *op)
         return _PyLong_AsUnsignedLongMask(op);
     }
 
-    lo = _PyLong_FromNbInt(op);
+    lo = (PyLongObject *)_PyLong_FromNbIndexOrNbInt(op);
     if (lo == NULL)
         return (unsigned long)-1;
 
@@ -1229,7 +1296,7 @@ PyLong_AsLongLong(PyObject *vv)
         v = (PyLongObject *)vv;
     }
     else {
-        v = _PyLong_FromNbInt(vv);
+        v = (PyLongObject *)_PyLong_FromNbIndexOrNbInt(vv);
         if (v == NULL)
             return -1;
         do_decref = 1;
@@ -1344,7 +1411,7 @@ PyLong_AsUnsignedLongLongMask(PyObject *op)
         return _PyLong_AsUnsignedLongLongMask(op);
     }
 
-    lo = _PyLong_FromNbInt(op);
+    lo = (PyLongObject *)_PyLong_FromNbIndexOrNbInt(op);
     if (lo == NULL)
         return (unsigned long long)-1;
 
@@ -1384,7 +1451,7 @@ PyLong_AsLongLongAndOverflow(PyObject *vv, int *overflow)
         v = (PyLongObject *)vv;
     }
     else {
-        v = _PyLong_FromNbInt(vv);
+        v = (PyLongObject *)_PyLong_FromNbIndexOrNbInt(vv);
         if (v == NULL)
             return -1;
         do_decref = 1;