implement coercions involving instances properly

diff --git a/Objects/classobject.c b/Objects/classobject.c
index f18b4fb9a5f1cb8eadaae689629fb99f1cd1a1d4..1fc5d6951d14945351e7981d965e9eff8944ac27 100644 (file)
--- a/Objects/classobject.c
+++ b/Objects/classobject.c
@@ -924,6 +924,58 @@ halfbinop(v, w, opname, r_result, thisfunc, swapped)
        return *r_result == NULL ? -1 : 0;
 }
 
+static int
+instance_coerce(pv, pw)
+       object **pv;
+       object **pw;
+{
+       object *v = *pv;
+       object *w = *pw;
+       object *coerce;
+       object *args;
+       object *coerced;
+
+       coerce = getattr(v, "__coerce__");
+       if (coerce == NULL) {
+               /* No __coerce__ method: always OK */
+               err_clear();
+               INCREF(v);
+               INCREF(w);
+               return 0;
+       }
+       /* Has __coerce__ method: call it */
+       args = mkvalue("(O)", w);
+       if (args == NULL) {
+               return -1;
+       }
+       coerced = call_object(coerce, args);
+       DECREF(args);
+       DECREF(coerce);
+       if (coerced == NULL) {
+               /* __coerce__ call raised an exception */
+               return -1;
+       }
+       if (coerced == None) {
+               /* __coerce__ says "I can't do it" */
+               DECREF(coerced);
+               return 1;
+       }
+       if (!is_tupleobject(coerced) || gettuplesize(coerced) != 2) {
+               /* __coerce__ return value is malformed */
+               DECREF(coerced);
+               err_setstr(TypeError,
+                          "coercion should return None or 2-tuple");
+               return -1;
+       }
+       /* __coerce__ returned two new values */
+       *pv = gettupleitem(coerced, 0);
+       *pw = gettupleitem(coerced, 1);
+       INCREF(*pv);
+       INCREF(*pw);
+       DECREF(coerced);
+       return 0;
+}
+
 
 #define UNARY(funcname, methodname) \
 static object *funcname(self) instanceobject *self; { \
@@ -1018,7 +1070,7 @@ static number_methods instance_as_number = {
        0, /*nb_and*/
        0, /*nb_xor*/
        0, /*nb_or*/
-       0, /*nb_coerce*/
+       (coercion)instance_coerce, /*nb_coerce*/
        (unaryfunc)instance_int, /*nb_int*/
        (unaryfunc)instance_long, /*nb_long*/
        (unaryfunc)instance_float, /*nb_float*/