SF bug [#468061] __str__ ignored in str subclass.

object.c, PyObject_Str:  Don't try to optimize anything except exact
string objects here; in particular, let str subclasses go thru tp_str,
same as non-str objects.  This allows overrides of tp_str to take
effect.

stringobject.c:
+ string_print (str's tp_print):  If the argument isn't an exact string
  object, get one from PyObject_Str.

+ string_str (str's tp_str):  Make a genuine-string copy of the object if
  it's of a proper str subclass type.  str() applied to a str subclass
  that doesn't override __str__ ends up here.

test_descr.py:  New str_of_str_subclass() test.

2 files changed, 21 insertions, 8 deletions

diff --git a/Objects/object.c b/Objects/object.c
index be8eb07..af0c0bb 100644
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -261,12 +261,6 @@ PyObject_Str(PyObject *v)
 		Py_INCREF(v);
 		return v;
 	}
-	if (PyString_Check(v)) {
-		/* For a string subtype that's not a string, return a true
-		   string with the same string data. */
-		PyStringObject *s = (PyStringObject *)v;
-		return PyString_FromStringAndSize(s->ob_sval, s->ob_size);
-	}
 	if (v->ob_type->tp_str == NULL)
 		return PyObject_Repr(v);
 
diff --git a/Objects/stringobject.c b/Objects/stringobject.c
index aea31ac..0a3155e 100644
--- a/Objects/stringobject.c
+++ b/Objects/stringobject.c
@@ -566,7 +566,18 @@ string_print(PyStringObject *op, FILE *fp, int flags)
 	int i;
 	char c;
 	int quote;
+
 	/* XXX Ought to check for interrupts when writing long strings */
+	if (! PyString_CheckExact(op)) {
+		int ret;
+		/* A str subclass may have its own __str__ method. */
+		op = (PyStringObject *) PyObject_Str((PyObject *)op);
+		if (op == NULL)
+			return -1;
+		ret = string_print(op, fp, flags);
+		Py_DECREF(op);
+		return ret;
+	}
 	if (flags & Py_PRINT_RAW) {
 		fwrite(op->ob_sval, 1, (int) op->ob_size, fp);
 		return 0;
@@ -651,8 +662,16 @@ string_repr(register PyStringObject *op)
 static PyObject *
 string_str(PyObject *s)
 {
-	Py_INCREF(s);
-	return s;
+	assert(PyString_Check(s));
+	if (PyString_CheckExact(s)) {
+		Py_INCREF(s);
+		return s;
+	}
+	else {
+		/* Subtype -- return genuine string with the same value. */
+		PyStringObject *t = (PyStringObject *) s;
+		return PyString_FromStringAndSize(t->ob_sval, t->ob_size);
+	}
 }
 
 static int